Display Device, Display Module, Electronic Device, and Manufacturing Method of Display Device

ABSTRACT

A display device with a wide viewing angle is provided. A display device with a high aperture ratio is provided. The display device includes a first display element, a second display element, and an insulating layer. The first display element includes a first pixel electrode configured to reflect visible light. The second display element is configured to emit visible light. The second display element includes a second pixel electrode and a common electrode. The first pixel electrode is positioned on an opposite side of the insulating layer from the second pixel electrode. The common electrode is positioned on an opposite side of the second pixel electrode from the insulating layer. A shortest distance X between a first plane and a second plane is longer than or equal to 500 nm and shorter than or equal to 200 μm. The first plane includes a plane of the first pixel electrode on the insulating layer side in a display region of the first display element, and the second plane includes a plane of the common electrode on the insulating layer side in a display region of the second display element.

BACKGROUND OF THE INVENTION 1. Field of the Invention

One embodiment of the present invention relates to a display device, adisplay module, an electronic device, and a manufacturing method of adisplay device.

Note that one embodiment of the present invention is not limited to theabove technical field. Examples of the technical field of one embodimentof the present invention include a semiconductor device, a displaydevice, a light-emitting device, a power storage device, a memorydevice, an electronic device, a lighting device, an input device (suchas a touch sensor), an input/output device (such as a touch panel), adriving method thereof, and a manufacturing method thereof.

2. Description of the Related Art

Recent display devices have been expected to be applied to a variety ofuses. Light-emitting devices including light-emitting elements, liquidcrystal display devices including liquid crystal elements, and the likehave been developed as display devices.

Patent Document 1, for example, discloses a flexible light-emittingdevice to which an organic electroluminescent (EL) element is applied.

Patent Document 2 discloses a transflective liquid crystal displaydevice having a region reflecting visible light and a regiontransmitting visible light. The transflective liquid crystal displaydevice can be used as a reflective liquid crystal display device in anenvironment where sufficient external light can be obtained and as atransmissive liquid crystal display device in an environment wheresufficient external light cannot be obtained.

REFERENCE Patent Documents [Patent Document 1] Japanese Published PatentApplication No. 2014-197522 [Patent Document 2] Japanese PublishedPatent Application No. 2011-191750 SUMMARY OF THE INVENTION

An object of one embodiment of the present invention is to provide adisplay device with low power consumption. Another object of oneembodiment of the present invention is to provide a display device withhigh visibility regardless of the ambient brightness. Another object ofone embodiment of the present invention is to provide an all-weatherdisplay device. Another object of one embodiment of the presentinvention is to provide a display device with a wide viewing angle.Another object of one embodiment of the present invention is to providea display device with a high aperture ratio. Another object of oneembodiment of the present invention is to provide a display device withhigh light extraction efficiency. Another object of one embodiment ofthe present invention is to provide a display device with highconvenience. Another object of one embodiment of the present inventionis to reduce the thickness or weight of a display device. Another objectof one embodiment of the present invention is to provide a novel displaydevice, a novel input/output device, a novel electronic device, or thelike.

Note that the descriptions of these objects do not preclude theexistence of other objects. One embodiment of the present invention doesnot necessarily achieve all the objects. Other objects can be derivedfrom the description of the specification, the drawings, and the claims.

[1] One embodiment of the present invention is a display deviceincluding a first display element, a second display element, and aninsulating layer. The first display element includes a first pixelelectrode configured to reflect visible light. The second displayelement is configured to emit visible light. The second display elementincludes a second pixel electrode and a common electrode. The firstpixel electrode is positioned on an opposite side of the insulatinglayer from the second pixel electrode. The common electrode ispositioned on an opposite side of the second pixel electrode from theinsulating layer. A shortest distance X between a first plane and asecond plane is longer than or equal to 500 nm and shorter than or equalto 200 μm. The first plane includes a plane of the first pixel electrodeon the insulating layer side in a display region of the first displayelement, and the second plane includes a plane of the common electrodeon the insulating layer side in a display region of the second displayelement. The display device preferably includes a first transistor and asecond transistor. The first transistor is configured to control drivingof the first display element. The second transistor is configured tocontrol driving of the second display element. The insulating layer hasa portion serving as a gate insulating layer of the first transistor anda portion serving as a gate insulating layer of the second transistor.

[2] One embodiment of the present invention is a display deviceincluding a first display element, a second display element, a firstinsulating layer, a second insulating layer, a first transistor, and asecond transistor. The first transistor is configured to control drivingof the first display element. The second transistor is configured tocontrol driving of the second display element. The first display elementincludes a first pixel electrode configured to reflect visible light.The second display element is configured to emit visible light. Thesecond display element includes a second pixel electrode and a commonelectrode. The first transistor and the second transistor are positionedbetween the first insulating layer and the second insulating layer. Thefirst transistor is electrically connected to the first pixel electrodethrough an opening in the first insulating layer. The second transistoris electrically connected to the second pixel electrode through anopening in the second insulating layer. The common electrode ispositioned on an opposite side of the second pixel electrode from thesecond insulating layer. A shortest distance X between a first plane anda second plane is longer than or equal to 500 nm and shorter than orequal to 200 μm. The first plane includes a plane of the first pixelelectrode on the first transistor side in a display region of the firstdisplay element, and the second plane includes a plane of the commonelectrode on the second transistor side in a display region of thesecond display element. One or both of the first transistor and thesecond transistor preferably include an oxide semiconductor in a channelformation region. The display device preferably includes an opticalmember. A shortest distance between the optical member and the firsttransistor is longer than a shortest distance between the optical memberand the first display element. A shortest distance between the opticalmember and the second display element is longer than the shortestdistance between the optical member and the first transistor. Theoptical member preferably includes at least one of a polarizing plate, alight diffusion layer, and an anti-reflective layer.

In [1] or [2], the shortest distance X is preferably longer than orequal to 1 μm and shorter than or equal to 20 μm.

In [1] or [2], the first pixel electrode may include an opening. In thatcase, the second display element includes a region overlapping with theopening. The second display element is configured to emit visible lightto the opening.

[3] One embodiment of the present invention is a display deviceincluding a first display element, a second display element, and aninsulating layer. The first display element is configured to reflectvisible light. The second display element is configured to emit visiblelight. The first display element is positioned on an opposite side ofthe insulating layer from the second display element. When a viewer seesthe display device from a direction inclined by 85° from a directionperpendicular to a display surface of the display device, the viewer cansee 10% or more of the area of a display region of the second displayelement. When a viewer sees the display device from a direction inclinedby 30° from the direction perpendicular to the display surface of thedisplay device, the viewer can see 100% of the area of the displayregion of the second display element.

[4] One embodiment of the present invention is the display device in[3], which has the following characteristics. The first display elementincludes a first pixel electrode configured to reflect visible light.The second display element includes a second pixel electrode and acommon electrode. The first pixel electrode is positioned on an oppositeside of the insulating layer from the second pixel electrode. The commonelectrode is positioned on an opposite side of the second pixelelectrode from the insulating layer.

[5] One embodiment of the present invention is the display device in[4], which has the following characteristics. The first pixel electrodeincludes an opening. The second display element includes a regionoverlapping with the opening. The second display element is configuredto emit visible light to the opening.

[6] One embodiment of the present invention is the display device in[5], which has the following characteristics. The display devicesatisfies Formula (1), Formula (2), Formula (3), and Formula (4). Afirst plane includes a plane of the first pixel electrode on an oppositeside of the insulating layer in a display region of the first displayelement. A second plane includes a plane of the common electrode on theinsulating layer side in a display region of the second display element.

$\begin{matrix}{\lbrack {{Formulae}\mspace{14mu} 1} \rbrack \mspace{616mu}} & \; \\{{D\; \tan \; \theta_{1}} \leq {{\frac{9}{10}L} + A}} & (1) \\{\frac{\sin \; \theta_{1}}{\sin \; 85{^\circ}} = \frac{1}{N}} & (2) \\{{D\; \tan \; \theta_{2}} \leq A} & (3) \\{\frac{\sin \; \theta_{2}}{\sin \; 30{^\circ}} = \frac{1}{N}} & (4)\end{matrix}$

In the above formulae, A, which is greater than or equal to 0,represents the length between an end portion of the first pixelelectrode and a foot of a perpendicular drawn from an end portion of thedisplay region of the second display element to the first plane.Furthermore, D represents the shortest distance between the first planeand the second plane, and L represents the width of the second pixelelectrode. In addition, N, which is greater than or equal to 1,represents the refractive index between the first plane and the secondplane in the region overlapping with the opening. Each of θ₁ and θ₂represents an angle formed by a perpendicular from the second plane tothe first plane and incident light from the second display element tothe first plane.

In [6], a stacked-layer structure of a layers may be included betweenthe first plane and the second plane and in the region overlapping withthe opening. In this case, N satisfies Formula (5).

$\begin{matrix}{\lbrack {{Formula}\mspace{14mu} 2} \rbrack \mspace{625mu}} & \; \\{N = \frac{\sum\limits_{x = 1}^{a}\; {N_{x}D_{x}}}{D}} & (5)\end{matrix}$

In the above formula, a is an integer greater than or equal to 2, and xis an integer greater than or equal to 1 and less than or equal to a.Furthermore, D_(x) represents the thickness of an x-th layer in thestacked-layer structure, and N_(x), which is greater than or equal to 1,represents the refractive index of the x-th layer in the stacked-layerstructure.

[7] One embodiment of the present invention is the display device in[5], which has the following characteristics. A stacked-layer structureof a layers is included between a first plane and a second plane and inthe region overlapping with the opening. The display device satisfiesFormula (6), Formula (7), Formula (8), and Formula (9). The first planeincludes a plane of the first pixel electrode on an opposite side of theinsulating layer in a display region of the first display element. Thesecond plane includes a plane of the common electrode on the insulatinglayer side in a display region of the second display element.

$\begin{matrix}{\lbrack {{Formulae}\mspace{14mu} 3} \rbrack \mspace{616mu}} & \; \\{{\sum\limits_{x = 1}^{a}\; {D_{x}\; \tan \; \theta_{x}}} \leq {{\frac{9}{10}L} + A}} & (6) \\{\frac{\sin \; \theta_{x}}{\sin \; 85{^\circ}} = \frac{1}{N_{x}}} & (7) \\{{\sum\limits_{y = 1}^{a}\; {D_{y}\; \tan \; \theta_{y}}} \leq A} & (8) \\{\frac{\sin \; \theta_{y}}{\sin \; 30{^\circ}} = \frac{1}{N_{y}}} & (9)\end{matrix}$

In the above formulae, a is an integer greater than or equal to 2, andeach of x and y is an integer greater than or equal to 1 and less thanor equal to a. Note that A, which is greater than or equal to 0,represents the length between an end portion of the first pixelelectrode and a foot of a perpendicular drawn from an end portion of thedisplay region of the second display element to the first plane.Furthermore, D_(x) represents the thickness of an x-th layer in thestacked-layer structure, D_(y) represents the thickness of a y-th layerin the stacked-layer structure, and L represents the width of the secondpixel electrode. In addition, N_(x), which is greater than or equal to1, represents the refractive index of the x-th layer in thestacked-layer structure, and N_(y), which is greater than or equal to 1,represents the refractive index of the y-th layer in the stacked-layerstructure. Furthermore, θ_(x) represents an angle formed by aperpendicular from the second plane to the first plane and refractedlight of light emitted from the second display element that enters thex-th layer from an (x−1)-th layer, and θ_(y) represents an angle formedby the perpendicular from the second plane to the first plane andrefracted light of light emitted from the second display element thatenters the y-th layer from a (y−1)-th layer.

The display device in any one of [3] to [7] preferably includes a firsttransistor and a second transistor. The first transistor is configuredto control driving of the first display element. The second transistoris configured to control driving of the second display element. In thiscase, the insulating layer has a portion serving as a gate insulatinglayer of the first transistor and a portion serving as a gate insulatinglayer of the second transistor. One or both of the first transistor andthe second transistor preferably include an oxide semiconductor in achannel formation region.

The display device in any one of [3] to [7] preferably includes anoptical member. A shortest distance between the optical member and thefirst transistor is longer than a shortest distance between the opticalmember and the first display element. A shortest distance between theoptical member and the second display element is longer than theshortest distance between the optical member and the first transistor.The optical member preferably includes at least one of a polarizingplate, a light diffusion layer, and an anti-reflective layer.

Any of the above display devices is preferably configured to display animage using one or both of light reflected by the first display elementand light emitted from the second display element.

In any of the above display devices, the first display element ispreferably a reflective liquid crystal element.

In any of the above display devices, the second display element ispreferably an electroluminescent element.

One embodiment of the present invention is a display module includingany of the above display devices and a circuit board such as a flexibleprinted circuit (FPC).

One embodiment of the present invention is an electronic deviceincluding the above display module and at least one of an antenna, abattery, a housing, a camera, a speaker, a microphone, and an operationbutton.

One embodiment of the present invention is a method for manufacturing adisplay device including a first display element, a second displayelement, and an insulating layer. The first display element includes afirst pixel electrode configured to reflect visible light, a liquidcrystal layer, and a first common electrode configured to transmitvisible light. The second display element includes a second pixelelectrode configured to transmit visible light, a light-emitting layer,and a second common electrode configured to reflect visible light. Ashortest distance X between a first plane and a second plane is longerthan or equal to 500 nm and shorter than or equal to 200 μm. The firstplane includes a plane of the first pixel electrode on the insulatinglayer side in a display region of the first display element, and thesecond plane includes a plane of the second common electrode on theinsulating layer side in a display region of the second display element.In the method for manufacturing the display device, the first commonelectrode is formed over a first substrate; the first pixel electrode isformed over a formation substrate; the insulating layer is formed overthe first pixel electrode; the second pixel electrode, thelight-emitting layer, and the second common electrode are formed in thisorder over the insulating layer to form the second display element; theformation substrate and a second substrate are bonded to each other withan adhesive; the formation substrate and the first pixel electrode areseparated from each other; and the liquid crystal layer is positionedbetween the first common electrode and the exposed first pixel electrodeand the first substrate and the second substrate are bonded to eachother with an adhesive to form the first display element.

In the above method for manufacturing a display device, after the firstpixel electrode is formed, an opening may be provided in the first pixelelectrode and the second display element may be formed in a regionoverlapping with the opening.

In the above method for manufacturing a display device, the adhesiveused to bond the first substrate and the second substrate to each othermay include a conductive particle. The first common electrode iselectrically connected to a conductive layer by the conductive particlewhen the first substrate and the second substrate are bonded to eachother. The conductive layer and the first pixel electrode are formed byprocessing one conductive film.

According to one embodiment of the present invention, a display devicewith low power consumption can be provided. According to one embodimentof the present invention, a display device with high visibilityregardless of the ambient brightness can be provided. According to oneembodiment of the present invention, an all-weather display device canbe provided. According to one embodiment of the present invention, adisplay device with a wide viewing angle can be provided. According toone embodiment of the present invention, a display device with a highaperture ratio can be provided. According to one embodiment of thepresent invention, a display device with high light extractionefficiency can be provided. According to one embodiment of the presentinvention, a display device with high convenience can be provided.According to one embodiment of the present invention, the thickness orweight of a display device can be reduced. According to one embodimentof the present invention, a novel display device, a novel input/outputdevice, a novel electronic device, or the like can be provided.

Note that the descriptions of these effects do not preclude theexistence of other effects. One embodiment of the present invention doesnot necessarily have all the effects. Other effects can be derived fromthe description of the specification, the drawings, and the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view illustrating an example of a displaydevice.

FIGS. 2A and 2B are cross-sectional views each illustrating a positionalrelationship between an electrode included in a liquid crystal elementand an electrode included in a light-emitting element.

FIGS. 3A and 3B are cross-sectional views each illustrating an exampleof a display device.

FIG. 4 is a perspective view illustrating an example of a displaydevice.

FIG. 5 is a cross-sectional view illustrating an example of a displaydevice.

FIG. 6 is a cross-sectional view illustrating an example of a displaydevice.

FIGS. 7A and 7B are cross-sectional views each illustrating an exampleof a display device.

FIGS. 8A to 8E are cross-sectional views illustrating examples oftransistors.

FIGS. 9A to 9D are cross-sectional views illustrating an example of amanufacturing method of a display device.

FIGS. 10A to 10C are cross-sectional views illustrating an example of amanufacturing method of a display device.

FIGS. 11A and 11B are cross-sectional views illustrating an example of amanufacturing method of a display device.

FIGS. 12A and 12B are cross-sectional views illustrating an example of amanufacturing method of a display device.

FIGS. 13A and 13B are cross-sectional views each illustrating apositional relationship between an electrode included in a liquidcrystal element and an electrode included in a light-emitting element.

FIG. 14 is a cross-sectional view illustrating a positional relationshipbetween an electrode included in a liquid crystal element and anelectrode included in a light-emitting element.

FIGS. 15A and 15B are cross-sectional views each illustrating apositional relationship between an electrode included in a liquidcrystal element and an electrode included in a light-emitting element.

FIG. 16 is a cross-sectional view illustrating an example of a displaydevice.

FIG. 17 is a cross-sectional view illustrating an example of a displaydevice.

FIGS. 18A and 18B are cross-sectional views each illustrating an exampleof a display device.

FIG. 19 is a block diagram illustrating an example of a display device.

FIGS. 20A to 20C each illustrate an example of a pixel unit.

FIGS. 21A to 21C each illustrate an example of a pixel unit.

FIGS. 22A to 22C each illustrate an example of a pixel unit.

FIG. 23A illustrates an example of a display device, and FIGS. 23B1,23B2, 23B3, and 23B4 each illustrate an example of a pixel.

FIG. 24 is a circuit diagram illustrating an example of a pixel circuitin a display device.

FIG. 25A is a circuit diagram illustrating an example of a pixel circuitin a display device, and FIG. 25B is a diagram illustrating an exampleof a pixel.

FIG. 26 illustrates an example of a display module.

FIGS. 27A to 27D illustrate examples of electronic devices.

FIGS. 28A to 28E illustrate examples of electronic devices.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments will be described in detail with reference to drawings. Notethat the present invention is not limited to the following description,and it is easily understood by those skilled in the art that variouschanges and modifications can be made without departing from the spiritand scope of the present invention. Accordingly, the present inventionshould not be interpreted as being limited to the description of theembodiments below.

Note that in the structures of the invention described below, the sameportions or portions having similar functions are denoted by the samereference numerals in different drawings, and description of suchportions is not repeated. Further, the same hatching pattern is appliedto portions having similar functions, and the portions are not denotedby reference numerals in some cases.

The position, size, range, or the like of each structure illustrated indrawings is not accurately represented in some cases for easyunderstanding. Therefore, the disclosed invention is not necessarilylimited to the position, size, range, or the like disclosed in thedrawings.

Note that the terms “film” and “layer” can be interchanged with eachother depending on the case or circumstances. For example, the term“conductive layer” can be changed into the term “conductive film,” andthe term “insulating film” can be changed into the term “insulatinglayer.”

In this specification and the like, a metal oxide means an oxide ofmetal in a broad sense. Metal oxides are classified into an oxideinsulator, an oxide conductor (including a transparent oxide conductor),an oxide semiconductor (also simply referred to as an OS), and the like.For example, a metal oxide used in an active layer of a transistor iscalled an oxide semiconductor in some cases. In other words, an OS FETis a transistor including a metal oxide or an oxide semiconductor.

In this specification and the like, a metal oxide including nitrogen isalso called a metal oxide in some cases. Moreover, a metal oxideincluding nitrogen may be called a metal oxynitride.

In this specification and the like, “c-axis aligned crystal (CAAC)” or“cloud-aligned composite (CAC)” might be stated. CAAC refers to anexample of a crystal structure, and CAC refers to an example of afunction or a material composition.

An example of a crystal structure of an oxide semiconductor or a metaloxide is described. Note that an oxide semiconductor deposited by asputtering method using an In—Ga—Zn oxide target (In:Ga:Zn=4:2:4.1 in anatomic ratio) is described below as an example. An oxide semiconductorformed by a sputtering method using the above-mentioned target at asubstrate temperature of higher than or equal to 100° C. and lower thanor equal to 130° C. is referred to as sIGZO, and an oxide semiconductorformed by a sputtering method using the above-mentioned target with thesubstrate temperature set at room temperature (R.T.) is referred to astIGZO. For example, sIGZO has one or both crystal structures of nanocrystal (nc) and CAAC. Furthermore, tIGZO has a crystal structure of nc.Note that room temperature (R.T.) herein also refers to a temperature ofthe time when a substrate is not heated intentionally.

In this specification and the like, CAC-OS or CAC-metal oxide has afunction of a conductor in a part of the material and has a function ofa dielectric (or insulator) in another part of the material; as a whole,CAC-OS or CAC-metal oxide has a function of a semiconductor. In the casewhere CAC-OS or CAC-metal oxide is used in an active layer of atransistor, the conductor has a function of letting electrons (or holes)serving as carriers flow, and the dielectric has a function of notletting electrons serving as carriers flow. By the complementary actionof the function as a conductor and the function as a dielectric, CAC-OSor CAC-metal oxide can have a switching function (on/off function). Inthe CAC-OS or CAC-metal oxide, separation of the functions can maximizeeach function.

In this specification and the like, CAC-OS or CAC-metal oxide includesconductor regions and dielectric regions. The conductor regions have theabove-described function of the conductor, and the dielectric regionshave the above-described function of the dielectric. In some cases, theconductor regions and the dielectric regions in the material areseparated at the nanoparticle level. In some cases, the conductorregions and the dielectric regions are unevenly distributed in thematerial. When observed, the conductor regions are coupled in acloud-like manner with their boundaries blurred, in some cases.

In other words, CAC-OS or CAC-metal oxide can be called a matrixcomposite or a metal matrix composite.

Furthermore, in the CAC-OS or CAC-metal oxide, the conductor regions andthe dielectric regions each have a size of more than or equal to 0.5 nmand less than or equal to nm, preferably more than or equal to 0.5 nmand less than or equal to 3 nm and are dispersed in the material, insome cases.

Embodiment 1

In this embodiment, a display device of one embodiment of the presentinvention will be described with reference to FIG. 1, FIGS. 2A and 2B,FIGS. 3A and 3B, FIG. 4, FIG. 5, FIG. 6, FIGS. 7A and 7B, FIGS. 8A to8E, FIGS. 9A to 9D, FIGS. 10A to 10C, FIGS. 11A and 11B, and FIGS. 12Aand 12B.

The display device of this embodiment includes a first display elementreflecting visible light and a second display element emitting visiblelight.

The display device of this embodiment has a function of displaying animage using one or both of light reflected by the first display elementand light emitted from the second display element.

As the first display element, an element which displays an image byreflecting external light can be used. Such an element does not includea light source (or does not require an artificial light source); thus,power consumed in displaying an image can be significantly reduced.

As a typical example of the first display element, a reflective liquidcrystal element can be given. As the first display element, an elementusing a microcapsule method, an electrophoretic method, anelectrowetting method, an Electronic Liquid Powder (registeredtrademark) method, or the like can also be used, other than MicroElectro Mechanical Systems (MEMS) shutter element or an opticalinterference type MEMS element.

As the second display element, a light-emitting element is preferablyused. Since the luminance and the chromaticity of light emitted fromsuch a display element are not affected by external light, a clear imagethat has high color reproducibility (wide color gamut) and a highcontrast can be displayed.

As the second display element, a self-luminous light-emitting elementsuch as an organic light-emitting diode (OLED), a light-emitting diode(LED), or a quantum-dot light-emitting diode (QLED) can be used.

The display device of this embodiment has a first mode in which an imageis displayed using only the first display element, a second mode inwhich an image is displayed using only the second display element, and athird mode in which an image is displayed using both the first displayelement and the second display element. The display device of thisembodiment can be switched between these modes automatically ormanually.

In the first mode, an image is displayed using the first display elementand external light. Because a light source is unnecessary in the firstmode, power consumed in this mode is extremely low. When sufficientexternal light enters the display device (e.g., in a brightenvironment), for example, an image can be displayed by using lightreflected by the first display element. The first mode is effective inthe case where external light is white light or light near white lightand is sufficiently strong, for example. The first mode is suitable fordisplaying text. Furthermore, the first mode enables eye-friendlydisplay owing to the use of reflected external light, which leads to aneffect of easing eyestrain.

In the second mode, an image is displayed using light emitted from thesecond display element. Thus, an extremely vivid image (with highcontrast and excellent color reproducibility) can be displayedregardless of the illuminance and the chromaticity of external light.The second mode is effective in the case of extremely low illuminance,such as in a night environment or in a dark room, for example. When abright image is displayed in a dark environment, a user may feel thatthe image is too bright. To prevent this, an image with reducedluminance is preferably displayed in the second mode. In that case,glare can be reduced, and power consumption can also be reduced. Thesecond mode is suitable for displaying a vivid (still and moving) imageor the like.

In the third mode, an image is displayed using both light reflected bythe first display element and light emitted from the second displayelement. An image displayed in the third mode can be more vivid than animage displayed in the first mode while power consumption can be lowerthan that in the second mode. The third mode is effective in the casewhere the illuminance is relatively low or in the case where thechromaticity of external light is not white, for example, in anenvironment under indoor illumination or in the morning or evening.

With such a structure, an all-weather display device or a highlyconvenient display device with high visibility regardless of the ambientbrightness can be fabricated.

FIG. 1 is a cross-sectional view of a display device 10. The displaydevice 10 includes a liquid crystal element 180 as the first displayelement and a light-emitting element 170 as the second display element.

The display device 10 illustrated in FIG. 1 includes the liquid crystalelement 180, the light-emitting element 170, a transistor 41, atransistor 42, and the like between a pair of substrates (a substrate351 and a substrate 361).

The liquid crystal element 180 includes an electrode 311 having afunction of reflecting visible light, a liquid crystal layer 112, and anelectrode 113 having a function of transmitting visible light. Theliquid crystal layer 112 is positioned between the electrode 311 and theelectrode 113.

The liquid crystal element 180 has a function of reflecting visiblelight. The liquid crystal element 180 reflects light 22 to the substrate361 side.

The electrode 311 is electrically connected to a source or a drain ofthe transistor 41 through an opening provided in an insulating layer220. The electrode 311 functions as a pixel electrode. The electrode 113is electrically connected to a conductive layer 235 via a connector 243.The electrode 311 and the conductive layer 235 can be formed byprocessing one conductive film.

The light-emitting element 170 includes an electrode 191, an EL layer192, and an electrode 193. The EL layer 192 is positioned between theelectrode 191 and the electrode 193. The EL layer 192 contains at leasta light-emitting substance. The electrode 191 has a function oftransmitting visible light. The electrode 193 preferably has a functionof reflecting visible light.

The light-emitting element 170 has a function of emitting visible light.Specifically, the light-emitting element 170 is an electroluminescentelement that emits light to the substrate 361 side (light emission 21)when voltage is applied between the electrode 191 and the electrode 193.

The electrode 191 is electrically connected to a source or a drain ofthe transistor 42 through an opening provided in an insulating layer214. The electrode 191 functions as a pixel electrode. An end portion ofthe electrode 191 is covered with an insulating layer 216.

The light-emitting element 170 is preferably covered with an insulatinglayer 194. In FIG. 1, the insulating layer 194 is provided in contactwith the electrode 193. The insulating layer 194 can prevent an impurityfrom entering the light-emitting element 170, leading to an increase inthe reliability of the light-emitting element 170. The insulating layer194 and the substrate 351 are bonded to each other with an adhesivelayer 142.

The transistor 41 and the transistor 42 are positioned on the sameplane. The transistor 41 has a function of controlling the driving ofthe liquid crystal element 180. The transistor 42 has a function ofcontrolling the driving of the light-emitting element 170.

A circuit electrically connected to the liquid crystal element 180 and acircuit electrically connected to the light-emitting element 170 arepreferably formed on the same plane. In that case, the thickness of thedisplay device can be smaller than that in the case where the twocircuits are formed on different planes. Furthermore, since twotransistors can be formed in the same process, a manufacturing processcan be simplified as compared to the case where two transistors areformed on different planes.

The electrode 311, which serves as the pixel electrode of the liquidcrystal element 180, is positioned on the opposite side of a gateinsulating layer included in the transistors 41 and 42 from theelectrode 191, which serves as the pixel electrode of the light-emittingelement 170.

In the case where a transistor including an oxide semiconductor in itschannel formation region and having extremely low off-state current isused as the transistor 41 or in the case where a memory elementelectrically connected to the transistor 41 is used, for example, indisplaying a still image using the liquid crystal element 180, even ifwriting operation to a pixel is stopped, the gray level can bemaintained. In other words, an image can be kept displayed even with anextremely low frame rate. In one embodiment of the present invention,the frame rate can be extremely low and driving with low powerconsumption can be performed.

A distance X in FIG. 1 is the shortest distance between a first planeand a second plane. The first plane includes a plane of the electrode311 on the substrate 351 side in a display region of the liquid crystalelement 180, and the second plane includes a plane of the electrode 193on the substrate 361 side in a display region of the light-emittingelement 170. Note that the electrode 311 is a layer having a function ofreflecting visible light, which is included in the liquid crystalelement 180. The electrode 193 is a layer having a function ofreflecting visible light, which is included in the light-emittingelement 170. The electrode 193 can reflect light emitted from the ELlayer 192. Thus, the distance X can be determined with reference to theelectrode 193. Note that the display region of the display element is aregion contributing to displaying an image in the display element.

As illustrated in FIGS. 2A and 2B, when the display device is seen fromthe direction inclined toward the left or right by an angle θ from thedirection perpendicular to a display surface, which is regarded as 0°, alight-emitting region of the light-emitting element 170 is partiallyblocked from view by the electrode 311, in some cases. When lightemitted from the light-emitting element 170 is partially blocked by theelectrode 311, the luminance of an image that a viewer sees is lowerthan that in the case of seeing from the direction perpendicular to thedisplay surface (θ=0°). FIGS. 2A and 2B illustrate only the electrode193 of the light-emitting element 170 for easy description.

The proportion of the display region of the light-emitting element 170that is blocked from view by the electrode 311 when the display deviceis seen from the direction inclined by the angle θ is the same (orviewing angle characteristics are the same) in FIGS. 2A and 2B. At thesame time, a distance X2 in FIG. 2B is longer than a distance X1 in FIG.2A. In that case, a length L2 in FIG. 2B is longer than a length L1 inFIG. 2A.

A length L₀ shown in FIG. 1 corresponds to, for example, the length of aregion where the electrode 311 is not provided, e.g., the length of anopening in the electrode 311. The shorter the length L₀ is, the largerthe area of the electrode 311 in each pixel can be. Accordingly, theaperture ratio of the liquid crystal element 180 can be increased.

In the case where the viewing angle characteristics of the displaydevice are the same as illustrated in FIGS. 2A and 2B, the length L₀ canbe made shorter as the distance X becomes shorter. When the length L₀ isfixed, the viewing angle can be increased as the distance X becomesshorter.

In the display device of this embodiment, the distance X is preferablygreater than or equal to 500 nm and less than or equal to 200 μm,further preferably greater than or equal to 1 μm and less than or equalto 100 μm, and still further preferably greater than or equal to 1 μmand less than or equal to 20 μm. When the distance X is short, highviewing angle characteristics of the display device and a high apertureratio of the liquid crystal element 180 can be both achieved. Inaddition, since the length L₀ can be made short, the aperture ratio ofthe liquid crystal element 180 can be increased and the total apertureratio of the liquid crystal element 180 and the light-emitting element170 can be increased.

If the distance X is too short, the distance between the transistor andthe electrode in the display element is shortened, which might cause anincrease in parasitic capacitance. Thus, the distance X is preferablygreater than or equal to 500 nm. To reduce the parasitic capacitancebetween the electrode 311 and the transistor, the thickness of theinsulating layer 220 is preferably greater than or equal to 200 nm, andfurther preferably greater than or equal to 500 nm.

The shorter the distance X is, the shorter the distance from the displaysurface (which is on the substrate 361 side) of the display device 10 tothe electrode 193 can be. Accordingly, the luminance of thelight-emitting element 170 can be increased, and the light extractionefficiency of the display device 10 can be increased.

In a structure formed by simply bonding a display panel including theliquid crystal element 180 and a display panel including thelight-emitting element 170 to each other, a thick layer (mainly used asa substrate) made of glass, a resin, or the like is positioned betweenthe liquid crystal element 180 and the light-emitting element 170; thus,it is difficult to make the distance X short. The display device of thisembodiment does not include a substrate between the liquid crystalelement 180 and the light-emitting element 170. Thus, the distance X canbe short.

FIGS. 3A and 3B are specific cross-sectional views each illustrating theliquid crystal layer 112 and components around the liquid crystal layer112. In each of FIGS. 3A and 3B, the liquid crystal layer 112 ispositioned between an alignment film 133 a and an alignment film 133 b.As illustrated in FIG. 3A, the electrode 311 is embedded in theinsulating layer 220 in the display device of this embodiment. A planeof the electrode 311 on the liquid crystal layer 112 side and a plane ofthe insulating layer 220 on the liquid crystal layer 112 side can formthe same plane (or the same surface). That is, the plane of theelectrode 311 on the liquid crystal layer 112 side and the plane of theinsulating layer 220 on the liquid crystal layer 112 side are positionedon the same plane or in contact with the same plane, or the planes havethe same height or have (substantially) no step difference at theboundary, for example. Furthermore, the alignment film 133 a is providedflatly.

Meanwhile, in a comparative example illustrated in FIG. 3B, theelectrode 311 is provided on the plane of the insulating layer 220 onthe liquid crystal layer 112 side. The alignment film 133 a has anuneven surface (see portions in dashed-dotted frames) due to thethickness of the electrode 311. Near an end portion of the electrode311, the initial alignment of the liquid crystal layer 112 is more proneto variation due to the uneven surface of the alignment film 133 a insome cases. When such a region of the liquid crystal layer 112 that ismore prone to initial alignment variation is used for displaying animage, the contrast might degrade. Furthermore, in the case where theregion of the liquid crystal layer 112 that is more prone to initialalignment variation exists between two adjacent pixels, the degradationin contrast can be reduced by covering the region with a light-blockinglayer or the like. However, this might reduce the aperture ratio.

As illustrated in FIG. 3A, the alignment film 133 a is provided flat inthe display device of this embodiment; thus, a defect is less likely tooccur in alignment treatment such as rubbing treatment, and the initialalignment can be made uniform more easily even near the end portion ofthe electrode 311. Providing the alignment film 133 a flatly can reducethe generation of the region prone to the initial alignment variation ofthe liquid crystal layer 112 between two adjacent pixels. Thus, theaperture ratio can be increased, and the display device can easilyachieve a high resolution.

Here, an example of a method for manufacturing the display device 10illustrated in FIG. 1 is described. Note that the specific descriptionof the method for manufacturing the display device of this embodimentwill be described later. First, the electrode 311, the transistors 41and 42, and the light-emitting element 170 are formed in this order overa formation substrate. Next, the formation substrate and the substrate351 are bonded to each other. After that, the formation substrate andthe substrate 351 are separated from each other, so that the electrode311, the transistors 41 and 42, the light-emitting element 170, and thelike are transferred from the formation substrate to the substrate 351.Then, the substrate 351 and the substrate 361 over which the electrode113 and the like are provided are bonded to each other with the liquidcrystal layer 112 provided therebetween. In this manner, the displaydevice can be fabricated.

Since the electrode 311 is formed before the transistor 41, theelectrode 311 can be formed flat without being influenced by theunevenness due to the transistor 41 and a contact portion between theelectrode 311 and the transistor 41.

In the case where the transistor 41 and the light-emitting element 170are formed before the electrode 311, to reduce the unevenness due to thetransistor 41 and the light-emitting element 170, it is necessary toform a planarization film over the transistor 41 or the light-emittingelement 170 and to form the electrode 311 over the planarization film.In that case, the electrode 311 and the transistor 41 are connected toeach other through an opening in the planarization film and the contactportion therebetween forms a step, leading to a reduction in apertureratio.

When the electrode 311 is formed before the transistor 41 and thelight-emitting element 170, the planarization film is unnecessary.Specifically, the thickness of the insulating layer 220 can be reduced.Accordingly, the distance between the electrode 311 and the transistor41 and the distance between the electrode 311 and the light-emittingelement 170 can be shortened.

As described above, in the display device of this embodiment, formingthe pixel electrode of the liquid crystal element flat can reducevariation of the initial alignment of the liquid crystal layer. Thus, adisplay defect in the display device can be inhibited. Furthermore, areduction in aperture ratio due to the alignment defect of the liquidcrystal layer can be inhibited.

Since the distance between the pixel electrode of the liquid crystalelement and the light-emitting element can be shortened in the displaydevice of this embodiment, high viewing angle characteristics of thedisplay device and a high aperture ratio of the liquid crystal elementcan be both achieved. In addition, the total aperture ratio of theliquid crystal element and the light-emitting element can be increased.

Next, structure examples of the display device of this embodiment willbe described with reference to FIG. 4, FIG. 5, FIG. 6, and FIGS. 7A and7B.

Structure Example 1

FIG. 4 is a schematic perspective view of a display device 300. In thedisplay device 300, the substrate 351 and the substrate 361 are bondedto each other. In FIG. 4, the substrate 361 is denoted by a dashed line.

The display device 300 includes a display portion 362, a circuit 364, awiring 365, and the like. FIG. 4 illustrates an example in which thedisplay device 300 is provided with an integrated circuit (IC) 373 andan FPC 372. Thus, the structure illustrated in FIG. 4 can be regarded asa display module including the display device 300, the IC, and the FPC.

As the circuit 364, for example, a scan line driver circuit can be used.

The wiring 365 has a function of supplying a signal and power to thedisplay portion 362 and the circuit 364. The signal and power are inputto the wiring 365 from the outside through the FPC 372 or from the IC373.

FIG. 4 illustrates an example in which the IC 373 is provided over thesubstrate 351 by a chip on glass (COG) method, a chip on film (COF)method, or the like. An IC including a scan line driver circuit, asignal line driver circuit, or the like can be used as the IC 373, forexample. Note that the display device 300 and the display module are notnecessarily provided with an IC. The IC may be provided over the FPC bya COF method or the like.

FIG. 4 illustrates an enlarged view of part of the display portion 362.Electrodes 311 b included in a plurality of display elements arearranged in a matrix in the display portion 362. The electrode 311 b hasa function of reflecting visible light, and serves as a reflectiveelectrode of the liquid crystal element 180.

As illustrated in FIG. 4, the electrode 311 b includes an opening 451.In addition, the display portion 362 includes the light-emitting element170 that is positioned closer to the substrate 351 than the electrode311 b. Light from the light-emitting element 170 is emitted to thesubstrate 361 side through the opening 451 in the electrode 311 b. Thearea of the light-emitting region of the light-emitting element 170 maybe equal to the area of the opening 451. One of the area of thelight-emitting region of the light-emitting element 170 and the area ofthe opening 451 is preferably larger than the other because a margin formisalignment can be increased. It is particularly preferable that thearea of the opening 451 be larger than the area of the light-emittingregion of the light-emitting element 170. When the area of the opening451 is small, part of light from the light-emitting element 170 isblocked by the electrode 311 b and cannot be extracted to the outside,in some cases. The opening 451 with a sufficiently large area can reducewaste of light emitted from the light-emitting element 170.

FIG. 5 illustrates an example of cross-sections of part of a regionincluding the FPC 372, part of a region including the circuit 364, andpart of a region including the display portion 362 of the display device300 illustrated in FIG. 4.

The display device 300 illustrated in FIG. 5 includes a transistor 201,a transistor 203, a transistor 205, a transistor 206, the liquid crystalelement 180, the light-emitting element 170, the insulating layer 220, acoloring layer 131, a coloring layer 134, and the like, between thesubstrate 351 and the substrate 361. The substrate 361 and theinsulating layer 220 are bonded to each other with an adhesive layer141. The substrate 351 and the insulating layer 220 are bonded to eachother with the adhesive layer 142.

The substrate 361 is provided with the coloring layer 131, alight-blocking layer 132, an insulating layer 121, the electrode 113functioning as a common electrode of the liquid crystal element 180, thealignment film 133 b, an insulating layer 117, and the like. Apolarizing plate 135 is provided on an outer surface of the substrate361. The insulating layer 121 may have a function of a planarizationlayer. The insulating layer 121 enables the electrode 113 to have analmost flat surface, resulting in a uniform alignment state of a liquidcrystal layer 112. The insulating layer 117 serves as a spacer forholding a cell gap of the liquid crystal element 180. In the case wherethe insulating layer 117 transmits visible light, the insulating layer117 may be positioned to overlap with a display region of the liquidcrystal element 180.

The liquid crystal element 180 is a reflective liquid crystal element.The liquid crystal element 180 has a stacked-layer structure of anelectrode 311 a, the liquid crystal layer 112, and the electrode 113.The electrode 311 b that reflects visible light is provided in contactwith a surface of the electrode 311 a on the substrate 351 side. Theelectrode 311 b includes the opening 451. The electrode 311 a and theelectrode 113 transmit visible light. The alignment film 133 a isprovided between the liquid crystal layer 112 and the electrode 311 a.The alignment film 133 b is provided between the liquid crystal layer112 and the electrode 113.

In the liquid crystal element 180, the electrode 311 b has a function ofreflecting visible light, and the electrode 113 has a function oftransmitting visible light. Light entering from the substrate 361 sideis polarized by the polarizing plate 135, transmitted through theelectrode 113 and the liquid crystal layer 112, and reflected by theelectrode 311 b. Then, the light is transmitted through the liquidcrystal layer 112 and the electrode 113 again to reach the polarizingplate 135. In this case, alignment of a liquid crystal can be controlledwith a voltage that is applied between the electrode 311 b and theelectrode 113, and thus optical modulation of light can be controlled.In other words, the intensity of light emitted through the polarizingplate 135 can be controlled. Light excluding light in a particularwavelength region is absorbed by the coloring layer 131, and thus,emitted light is red light, for example.

As illustrated in FIG. 5, the electrode 311 a that transmits visiblelight is preferably provided across the opening 451. Accordingly, liquidcrystals in the liquid crystal layer 112 are aligned in a regionoverlapping with the opening 451 as in the other regions, in which casean alignment defect of the liquid crystals is prevented from beinggenerated in a boundary portion of these regions and undesired lightleakage can be suppressed.

At a connection portion 207, the electrode 311 b is electricallyconnected to a conductive layer 222 a included in the transistor 206 viaa conductive layer 221 b. The transistor 206 has a function ofcontrolling the driving of the liquid crystal element 180.

A connection portion 252 is provided in part of a region where theadhesive layer 141 is provided. In the connection portion 252, aconductive layer obtained by processing the same conductive film as theelectrode 311 a is electrically connected to part of the electrode 113with the connector 243. Accordingly, a signal or a potential input fromthe FPC 372 connected to the substrate 351 side can be supplied to theelectrode 113 formed on the substrate 361 side through the connectionportion 252.

As the connector 243, for example, a conductive particle can be used. Asthe conductive particle, a particle of an organic resin, silica, or thelike coated with a metal material can be used. It is preferable to usenickel or gold as the metal material because contact resistance can bedecreased. It is also preferable to use a particle coated with layers oftwo or more kinds of metal materials, such as a particle coated withnickel and further with gold. A material capable of elastic deformationor plastic deformation is preferably used for the connector 243. Asillustrated in FIG. 5, the connector 243, which is the conductiveparticle, has a shape that is vertically crushed in some cases. With thecrushed shape, the contact area between the connector 243 and aconductive layer electrically connected to the connector 243 can beincreased, thereby reducing contact resistance and suppressing thegeneration of problems such as disconnection.

The connector 243 is preferably provided so as to be covered with theadhesive layer 141. For example, the connectors 243 are dispersed in theadhesive layer 141 before curing of the adhesive layer 141.

The light-emitting element 170 is a bottom-emission light-emittingelement. The light-emitting element 170 has a stacked-layer structure inwhich the electrode 191, the EL layer 192, and the electrode 193 arestacked in this order from the insulating layer 220 side. The electrode191 is connected to the conductive layer 222 a included in thetransistor 205 through an opening provided in the insulating layer 214.The transistor 205 has a function of controlling the driving of thelight-emitting element 170. The insulating layer 216 covers an endportion of the electrode 191. The electrode 193 includes a material thatreflects visible light, and the electrode 191 includes a material thattransmits visible light. The insulating layer 194 is provided to coverthe electrode 193. Light is emitted from the light-emitting element 170to the substrate 361 side through the coloring layer 134, the insulatinglayer 220, the opening 451, the electrode 311 a, and the like.

The liquid crystal element 180 and the light-emitting element 170 canexhibit various colors when the color of the coloring layer varies amongpixels. The display device 300 can display a color image using theliquid crystal element 180. The display device 300 can display a colorimage using the light-emitting element 170.

The transistor 201, the transistor 203, the transistor 205, and thetransistor 206 are formed on a plane of the insulating layer 220 on thesubstrate 351 side. These transistors can be fabricated through the sameprocess.

The transistor 203 is used for controlling whether the pixel is selectedor not (such a transistor is also referred to as a switching transistoror a selection transistor). The transistor 205 is used for controllingcurrent flowing to the light-emitting element 170 (such a transistor isalso referred to as a driving transistor).

Insulating layers such as an insulating layer 211, an insulating layer212, an insulating layer 213, and the insulating layer 214 are providedon the substrate 351 side of the insulating layer 220. Part of theinsulating layer 211 functions as a gate insulating layer of eachtransistor. The insulating layer 212 is provided to cover the transistor206 and the like. The insulating layer 213 is provided to cover thetransistor 205 and the like. The insulating layer 214 functions as aplanarization layer. Note that the number of insulating layers coveringthe transistor is not limited and may be one or two or more.

A material through which impurities such as water or hydrogen do noteasily diffuse is preferably used for at least one of the insulatinglayers that cover the transistors. This is because such an insulatinglayer can serve as a barrier film. Such a structure can effectivelysuppress diffusion of the impurities into the transistors from theoutside, and a highly reliable display device can be provided.

Each of the transistors 201, 203, 205, and 206 includes a conductivelayer 221 a functioning as a gate, the insulating layer 211 functioningas the gate insulating layer, the conductive layer 222 a and aconductive layer 222 b functioning as a source and a drain, and asemiconductor layer 231. Here, a plurality of layers obtained byprocessing the same conductive film are shown with the same hatchingpattern.

The transistor 201 and the transistor 205 each include a conductivelayer 223 functioning as a gate, in addition to the components of thetransistor 203 or the transistor 206.

The structure in which the semiconductor layer where a channel is formedis provided between two gates is used as an example of the transistors201 and 205. Such a structure enables the control of the thresholdvoltages of transistors. The two gates may be connected to each otherand supplied with the same signal to operate the transistors. Suchtransistors can have higher field-effect mobility and thus have higheron-state current than other transistors. Consequently, a circuit capableof high-speed operation can be obtained. Furthermore, the area occupiedby a circuit portion can be reduced. The use of the transistor havinghigh on-state current can reduce signal delay in wirings and can reducedisplay unevenness even in a display device in which the number ofwirings is increased because of increase in size or definition.

Alternatively, by supplying a potential for controlling the thresholdvoltage to one of the two gates and a potential for driving to theother, the threshold voltage of the transistors can be controlled.

There is no limitation of the structure of the transistors included inthe display device. The transistor included in the circuit 364 and thetransistor included in the display portion 362 may have the samestructure or different structures. A plurality of transistors includedin the circuit 364 may have the same structure or a combination of twoor more kinds of structures. Similarly, a plurality of transistorsincluded in the display portion 362 may have the same structure or acombination of two or more kinds of structures.

It is preferable to use a conductive material containing an oxide forthe conductive layer 223. A conductive film used for the conductivelayer 223 is formed under an atmosphere containing oxygen, wherebyoxygen can be supplied to the insulating layer 212. The proportion of anoxygen gas in a deposition gas is preferably higher than or equal to 90%and lower than or equal to 100%. Oxygen supplied to the insulating layer212 is then supplied to the semiconductor layer 231 by later heattreatment; as a result, oxygen vacancies in the semiconductor layer 231can be reduced.

It is particularly preferable to use a low-resistance oxidesemiconductor for the conductive layer 223. In that case, an insulatingfilm that releases hydrogen, such as a silicon nitride film, ispreferably used for the insulating layer 213, for example, becausehydrogen can be supplied to the conductive layer 223 during theformation of the insulating layer 213 or by heat treatment performedafter the formation of the insulating layer 213, which leads to aneffective reduction in the electric resistance of the conductive layer223.

The coloring layer 134 is provided in contact with the insulating layer213. The coloring layer 134 is covered with the insulating layer 214.

A connection portion 204 is provided in a region where the substrate 351does not overlap with the substrate 361. In the connection portion 204,the wiring 365 is electrically connected to the FPC 372 via a connectionlayer 242. The connection portion 204 has a similar structure to theconnection portion 207. On the top surface of the connection portion204, a conductive layer obtained by processing the same conductive filmas the electrode 311 a is exposed. Thus, the connection portion 204 andthe FPC 372 can be electrically connected to each other via theconnection layer 242.

As the polarizing plate 135 provided on the outer surface of thesubstrate 361, a linear polarizing plate or a circularly polarizingplate can be used. An example of a circularly polarizing plate is astack including a linear polarizing plate and a quarter-wave retardationplate. Such a structure can reduce reflection of external light. Thecell gap, alignment, drive voltage, and the like of the liquid crystalelement used as the liquid crystal element 180 are controlled dependingon the kind of the polarizing plate so that desirable contrast isobtained.

Note that a variety of optical members can be arranged on the outersurface of the substrate 361. Examples of the optical members include apolarizing plate, a retardation plate, a light diffusion layer (e.g., adiffusion film), an anti-reflective layer, and a light-condensing film.Furthermore, an antistatic film preventing the attachment of dust, awater repellent film suppressing the attachment of stain, a hard coatfilm suppressing generation of a scratch caused by the use, or the likemay be arranged on the outer surface of the substrate 361.

For each of the substrates 351 and 361, glass, quartz, ceramic,sapphire, an organic resin, or the like can be used. When the substrates351 and 361 are formed using a flexible material, the flexibility of thedisplay device can be increased.

A liquid crystal element having, for example, a vertical alignment (VA)mode can be used as the liquid crystal element 180. Examples of thevertical alignment mode include a multi-domain vertical alignment (MVA)mode, a patterned vertical alignment (PVA) mode, and an advanced superview (ASV) mode.

A liquid crystal element having a variety of modes can be used as theliquid crystal element 180. For example, a liquid crystal element using,instead of a VA mode, a twisted nematic (TN) mode, an in-plane switching(IPS) mode, a fringe field switching (FFS) mode, an axially symmetricaligned micro-cell (ASM) mode, an optically compensated birefringence(OCB) mode, a ferroelectric liquid crystal (FLC) mode, anantiferroelectric liquid crystal (AFLC) mode, or the like can be used.

The liquid crystal element is an element that controls transmission ornon-transmission of light utilizing an optical modulation action of theliquid crystal. The optical modulation action of the liquid crystal iscontrolled by an electric field applied to the liquid crystal (includinga horizontal electric field, a vertical electric field, and an obliqueelectric field). As the liquid crystal used for the liquid crystalelement, a thermotropic liquid crystal, a low-molecular liquid crystal,a high-molecular liquid crystal, a polymer dispersed liquid crystal(PDLC), a ferroelectric liquid crystal, an anti-ferroelectric liquidcrystal, or the like can be used. Such a liquid crystal materialexhibits a cholesteric phase, a smectic phase, a cubic phase, a chiralnematic phase, an isotropic phase, or the like depending on conditions.

As the liquid crystal material, a positive liquid crystal or a negativeliquid crystal may be used, and an appropriate liquid crystal materialcan be used depending on the mode or design to be used.

To control the alignment of the liquid crystal, the alignment films canbe provided. In the case where a horizontal electric field mode isemployed, a liquid crystal exhibiting a blue phase for which analignment film is unnecessary may be used. The blue phase is one ofliquid crystal phases, which is generated just before a cholestericphase changes into an isotropic phase while the temperature of acholesteric liquid crystal is increased. Since the blue phase appearsonly in a narrow temperature range, a liquid crystal composition inwhich several weight percent or more of a chiral material is mixed isused for the liquid crystal in order to improve the temperature range.The liquid crystal composition that includes a liquid crystal exhibitinga blue phase and a chiral material has a short response time and hasoptical isotropy. In addition, the liquid crystal composition thatincludes a liquid crystal exhibiting a blue phase and a chiral materialdoes not need alignment treatment and has small viewing angledependence. An alignment film does not need to be provided and rubbingtreatment is thus not necessary; accordingly, electrostatic dischargedamage caused by the rubbing treatment can be prevented and defects anddamage of the liquid crystal display device in the manufacturing processcan be reduced.

In the case where the reflective liquid crystal element is used, thepolarizing plate 135 is provided on the display surface side. Inaddition, a light diffusion plate is preferably provided on the displaysurface side to improve visibility.

A front light may be provided on the outer side of the polarizing plate135. As the front light, an edge-light front light is preferably used. Afront light including an LED is preferably used to reduce powerconsumption.

As the adhesive layer, any of a variety of curable adhesives such as areactive curable adhesive, a thermosetting adhesive, an anaerobicadhesive, and a photocurable adhesive such as an ultraviolet curableadhesive can be used. Examples of these adhesives include an epoxyresin, an acrylic resin, a silicone resin, a phenol resin, a polyimideresin, an imide resin, a polyvinyl chloride (PVC) resin, a polyvinylbutyral (PVB) resin, and an ethylene vinyl acetate (EVA) resin. Inparticular, a material with low moisture permeability, such as an epoxyresin, is preferred. Alternatively, a two-component-mixture-type resinmay be used. Further alternatively, an adhesive sheet or the like may beused.

As the connection layer 242, an anisotropic conductive film (ACF), ananisotropic conductive paste (ACP), or the like can be used.

The light-emitting element 170 may be a top emission, bottom emission,or dual emission light-emitting element, or the like. A conductive filmthat transmits visible light is used as the electrode through whichlight is extracted. A conductive film that reflects visible light ispreferably used as the electrode through which light is not extracted.

The EL layer 192 includes at least a light-emitting layer. In additionto the light-emitting layer, the EL layer 192 may further include one ormore layers containing any of a substance with a high hole-injectionproperty, a substance with a high hole-transport property, ahole-blocking material, a substance with a high electron-transportproperty, a substance with a high electron-injection property, asubstance with a bipolar property (a substance with a high electron- andhole-transport property), and the like.

Either a low molecular compound or a high molecular compound can be usedfor the EL layer 192, and an inorganic compound may also be included.The layers included in the EL layer 192 can be formed by any of thefollowing methods: an evaporation method (including a vacuum evaporationmethod), a transfer method, a printing method, an inkjet method, acoating method, and the like.

The EL layer 192 may contain an inorganic compound such as quantum dots.When quantum dots are used for the light-emitting layer, quantum dotscan function as light-emitting materials, for example.

With the use of the combination of a color filter (coloring layer) and amicrocavity structure (optical adjustment layer), light with high colorpurity can be extracted from the display device. The thickness of theoptical adjustment layer varies depending on the color of the pixel.

As materials for a gate, a source, and a drain of a transistor, and aconductive layer such as a wiring or an electrode included in a displaydevice, any of metals such as aluminum, titanium, chromium, nickel,copper, yttrium, zirconium, molybdenum, silver, tantalum, and tungsten,or an alloy containing any of these metals as its main component can beused. A single-layer structure or multi-layer structure including a filmcontaining any of these materials can be used.

As a light-transmitting conductive material, a conductive oxide such asindium oxide, indium tin oxide, indium zinc oxide, zinc oxide, or zincoxide containing gallium, or graphene can be used. Alternatively, ametal material such as gold, silver, platinum, magnesium, nickel,tungsten, chromium, molybdenum, iron, cobalt, copper, palladium, ortitanium, or an alloy material containing any of these metal materialscan be used. Alternatively, a nitride of the metal material (e.g.,titanium nitride) or the like may be used. In the case of using themetal material or the alloy material (or the nitride thereof), thethickness is preferably set small enough to be able to transmit light.Alternatively, a stacked film of any of the above materials can be usedfor the conductive layers. For example, a stacked film of indium tinoxide and an alloy of silver and magnesium is preferably used becausethe conductivity can be increased. They can also be used for conductivelayers such as a variety of wirings and electrodes included in a displaydevice, and conductive layers (e.g., conductive layers serving as apixel electrode or a common electrode) included in a display element.

Examples of an insulating material that can be used for the insulatinglayers include a resin such as acrylic or epoxy resin, and an inorganicinsulating material such as silicon oxide, silicon oxynitride, siliconnitride oxide, silicon nitride, or aluminum oxide.

Examples of a material that can be used for the coloring layers includea metal material, a resin material, and a resin material containing apigment or dye.

Structure Example 2

A display device 300A illustrated in FIG. 6 is different from thedisplay device 300 mainly in that a transistor 281, a transistor 284, atransistor 285, and a transistor 286 are included instead of thetransistor 201, the transistor 203, the transistor 205, and thetransistor 206.

Note that the positions of the insulating layer 117, the connectionportion 207, and the like in FIG. 6 are different from those in FIG. 5.FIG. 6 illustrates an end portion of a pixel. The insulating layer 117is provided so as to overlap with an end portion of the coloring layer131 and an end portion of the light-blocking layer 132. As in thisstructure, the insulating layer 117 may be provided in a region notoverlapping with a display region (or in a region overlapping with thelight-blocking layer 132).

Two transistors included in the display device may partly overlap witheach other like the transistor 284 and the transistor 285. In that case,the area occupied by a pixel circuit can be reduced, leading to anincrease in resolution. Furthermore, the light-emitting area of thelight-emitting element 170 can be increased, leading to an improvementin aperture ratio. The light-emitting element 170 with a high apertureratio requires low current density to obtain necessary luminance; thus,the reliability is improved.

Each of the transistors 281, 284, and 286 includes the conductive layer221 a, the insulating layer 211, the semiconductor layer 231, theconductive layer 222 a, and the conductive layer 222 b. The conductivelayer 221 a overlaps with the semiconductor layer 231 with theinsulating layer 211 positioned therebetween. The conductive layer 222 aand the conductive layer 222 b are electrically connected to thesemiconductor layer 231. The transistor 281 includes the conductivelayer 223.

The transistor 285 includes the conductive layer 222 a, an insulatinglayer 217, a semiconductor layer 261, the conductive layer 223, theinsulating layer 212, the insulating layer 213, a conductive layer 263a, and a conductive layer 263 b. The conductive layer 222 a overlapswith the semiconductor layer 261 with the insulating layer 217positioned therebetween. The conductive layer 223 overlaps with thesemiconductor layer 261 with the insulating layers 212 and 213positioned therebetween. The conductive layer 263 a and the conductivelayer 263 b are electrically connected to the semiconductor layer 261.

The conductive layer 221 a functions as a gate. The insulating layer 211functions as a gate insulating layer. The conductive layer 222 aincluded in the transistor 286 functions as one of a source and a drain.The conductive layer 222 b functions as the other of the source and thedrain.

The conductive layer 222 a shared by the transistor 284 and thetransistor 285 has a portion functioning as one of a source and a drainof the transistor 284 and a portion functioning as a gate of thetransistor 285. The insulating layer 217, the insulating layer 212, andthe insulating layer 213 function as gate insulating layers. One of theconductive layer 263 a and the conductive layer 263 b functions as asource and the other functions as a drain. The conductive layer 223functions as a gate.

Structure Example 3

FIG. 7A is a cross-sectional view illustrating a display portion of adisplay device 300B.

The display device 300B is different from the display device 300 in thatthe coloring layer 131 is not provided. The transistor 203 is notillustrated in FIG. 7A. Other components are similar to those of thedisplay device 300 and thus are not described in detail.

The liquid crystal element 180 emits white light. Since the coloringlayer 131 is not provided, the display device 300B can display ablack-and-white image or a grayscale image using the liquid crystalelement 180.

Structure Example 4

A display device 300C illustrated in FIG. 7B is different from thedisplay device 300B in that the EL layer 192 is separately provided foreach color (the EL layer 192 is provided for each light-emitting element170) and the coloring layer 134 is not provided. Other components aresimilar to those of the display device 300B and thus are not describedin detail.

In the light-emitting element 170 employing a separate coloring method,at least one layer (typified by the light-emitting layer) included inthe EL layer 192 is separately provided for each color. All layersincluded in the EL layer may be separately provided for each color.

There is no particular limitation on the structure of the transistorincluded in the display device of one embodiment of the presentinvention. For example, a planar transistor, a staggered transistor, oran inverted staggered transistor may be used. A top-gate transistor or abottom-gate transistor may be used. Gate electrodes may be providedabove and below a channel.

FIGS. 8A to 8E illustrate structure examples of transistors.

A transistor 110 a illustrated in FIG. 8A is a top-gate transistor.

The transistor 110 a includes a conductive layer 221, the insulatinglayer 211, the semiconductor layer 231, the insulating layer 212, theconductive layer 222 a, and the conductive layer 222 b. Thesemiconductor layer 231 is provided over an insulating layer 151. Theconductive layer 221 overlaps with the semiconductor layer 231 with theinsulating layer 211 positioned therebetween. The conductive layer 222 aand the conductive layer 222 b are electrically connected to thesemiconductor layer 231 through openings provided in the insulatinglayer 211 and the insulating layer 212.

The conductive layer 221 functions as a gate. The insulating layer 211functions as a gate insulating layer. One of the conductive layer 222 aand the conductive layer 222 b functions as a source and the otherfunctions as a drain.

In the transistor 110 a, the conductive layer 221 can be physicallydistanced from the conductive layer 222 a or 222 b easily; thus, theparasitic capacitance between the conductive layer 221 and theconductive layer 222 a or 222 b can be reduced.

A transistor 110 b illustrated in FIG. 8B includes, in addition to thecomponents of the transistor 110 a, the conductive layer 223 and aninsulating layer 218. The conductive layer 223 is provided over theinsulating layer 151. The conductive layer 223 overlaps with thesemiconductor layer 231. The insulating layer 218 covers the conductivelayer 223 and the insulating layer 151.

The conductive layer 223 functions as one of a pair of gates. Thus, theon-state current of the transistor can be increased and the thresholdvoltage can be controlled.

FIGS. 8C to 8E each illustrate an example of a stacked-layer structureof two transistors. The structures of the two stacked transistors can beindependently determined, and the combination of the structures is notlimited to those illustrated in FIGS. 8C to 8E.

FIG. 8C illustrates a stacked-layer structure of a transistor 110 c anda transistor 110 d. The transistor 110 c includes two gates. Thetransistor 110 d has a bottom-gate structure. Note that the transistor110 c may have a structure including one gate (top-gate structure). Thetransistor 110 d may include two gates.

The transistor 110 c includes the conductive layer 223, the insulatinglayer 218, the semiconductor layer 231, the conductive layer 221, theinsulating layer 211, the conductive layer 222 a, and the conductivelayer 222 b. The conductive layer 223 is provided over the insulatinglayer 151. The conductive layer 223 overlaps with the semiconductorlayer 231 with the insulating layer 218 positioned therebetween. Theinsulating layer 218 covers the conductive layer 223 and the insulatinglayer 151. The conductive layer 221 overlaps with the semiconductorlayer 231 with the insulating layer 211 positioned therebetween.Although FIG. 8C illustrates an example where the insulating layer 211is provided only in a region overlapping with the conductive layer 221,the insulating layer 211 may be provided so as to cover an end portionof the semiconductor layer 231, as illustrated in FIG. 8B and otherdrawings. The conductive layer 222 a and the conductive layer 222 b areelectrically connected to the semiconductor layer 231 through openingsprovided in the insulating layer 212.

The transistor 110 d includes the conductive layer 222 b, the insulatinglayer 213, the semiconductor layer 261, the conductive layer 263 a, andthe conductive layer 263 b. The conductive layer 222 b includes a regionoverlapping with the semiconductor layer 261 with the insulating layer213 positioned therebetween. The insulating layer 213 covers theconductive layer 222 b. The conductive layer 263 a and the conductivelayer 263 b are electrically connected to the semiconductor layer 261.

The conductive layer 221 and the conductive layer 223 each function as agate of the transistor 110 c. The insulating layer 218 and theinsulating layer 211 each function as a gate insulating layer of thetransistor 110 c. The conductive layer 222 a functions as one of asource and a drain of the transistor 110 c.

The conductive layer 222 b has a portion functioning as the other of thesource and the drain of the transistor 110 c and a portion functioningas a gate of the transistor 110 d. The insulating layer 213 functions asa gate insulating layer of the transistor 110 d. One of the conductivelayer 263 a and the conductive layer 263 b functions as a source of thetransistor 110 d and the other functions as a drain of the transistor110 d.

The transistor 110 c and the transistor 110 d are preferably applied toa pixel circuit of the light-emitting element 170. For example, thetransistor 110 c can be used as a selection transistor and thetransistor 110 d can be used as a driving transistor.

The conductive layer 263 b is electrically connected to the electrode191 that functions as a pixel electrode of the light-emitting elementthrough an opening provided in the insulating layer 217 and theinsulating layer 214.

FIG. 8D illustrates a stacked-layer structure of a transistor 110 e anda transistor 110 f. The transistor 110 e has a bottom-gate structure.The transistor 110 f includes two gates. The transistor 110 e mayinclude two gates.

The transistor 110 e includes the conductive layer 221, the insulatinglayer 211, the semiconductor layer 231, the conductive layer 222 a, andthe conductive layer 222 b. The conductive layer 221 is provided overthe insulating layer 151. The conductive layer 221 overlaps with thesemiconductor layer 231 with the insulating layer 211 positionedtherebetween. The insulating layer 211 covers the conductive layer 221and the insulating layer 151. The conductive layer 222 a and theconductive layer 222 b are electrically connected to the semiconductorlayer 231.

The transistor 110 f includes the conductive layer 222 b, the insulatinglayer 212, the semiconductor layer 261, the conductive layer 223, theinsulating layer 218, the insulating layer 213, the conductive layer 263a, and the conductive layer 263 b. The conductive layer 222 b includes aregion overlapping with the semiconductor layer 261 with the insulatinglayer 212 positioned therebetween. The insulating layer 212 covers theconductive layer 222 b. The conductive layer 263 a and the conductivelayer 263 b are electrically connected to the semiconductor layer 261through openings provided in the insulating layer 213. The conductivelayer 223 overlaps with the semiconductor layer 261 with the insulatinglayer 218 positioned therebetween. The insulating layer 218 is providedin a region overlapping with the conductive layer 223.

The conductive layer 221 functions as a gate of the transistor 110 e.The insulating layer 211 functions as a gate insulating layer of thetransistor 110 e. The conductive layer 222 a functions as one of asource and a drain of the transistor 110 e.

The conductive layer 222 b has a portion functioning as the other of thesource and the drain of the transistor 110 e and a portion functioningas a gate of the transistor 110 f. The conductive layer 223 functions asanother gate of the transistor 110 f. The insulating layer 212 and theinsulating layer 218 each function as a gate insulating layer of thetransistor 110 f. One of the conductive layer 263 a and the conductivelayer 263 b functions as a source of the transistor 110 f and the otherfunctions as a drain of the transistor 110 f.

The conductive layer 263 b is electrically connected to the electrode191 that functions as a pixel electrode of a light-emitting elementthrough an opening provided in the insulating layer 214.

FIG. 8E illustrates a stacked-layer structure of a transistor 110 g anda transistor 110 h. The transistor 110 g has a top-gate structure. Thetransistor 110 h includes two gates. The transistor 110 g may includetwo gates.

The transistor 110 g includes the semiconductor layer 231, theconductive layer 221, the insulating layer 211, the conductive layer 222a, and the conductive layer 222 b. The semiconductor layer 231 isprovided over the insulating layer 151. The conductive layer 221overlaps with the semiconductor layer 231 with the insulating layer 211positioned therebetween. The insulating layer 211 overlaps with theconductive layer 221. The conductive layer 222 a and the conductivelayer 222 b are electrically connected to the semiconductor layer 231through openings provided in the insulating layer 212.

The transistor 110 h includes the conductive layer 222 b, the insulatinglayer 213, the semiconductor layer 261, the conductive layer 223, theinsulating layer 218, the insulating layer 217, the conductive layer 263a, and the conductive layer 263 b. The conductive layer 222 b includes aregion overlapping with the semiconductor layer 261 with the insulatinglayer 213 positioned therebetween. The insulating layer 213 covers theconductive layer 222 b. The conductive layer 263 a and the conductivelayer 263 b are electrically connected to the semiconductor layer 261through openings provided in the insulating layer 217. The conductivelayer 223 overlaps with the semiconductor layer 261 with the insulatinglayer 218 positioned therebetween. The insulating layer 218 is providedin a region overlapping with the conductive layer 223.

The conductive layer 221 functions as a gate of the transistor 110 g.The insulating layer 211 functions as a gate insulating layer of thetransistor 110 g. The conductive layer 222 a functions as one of asource and a drain of the transistor 110 g.

The conductive layer 222 b has a portion functioning as the other of thesource and the drain of the transistor 110 g and a portion functioningas a gate of the transistor 110 h. The conductive layer 223 functions asanother gate of the transistor 110 h. The insulating layer 212 and theinsulating layer 218 each function as a gate insulating layer of thetransistor 110 h. One of the conductive layer 263 a and the conductivelayer 263 b functions as a source of the transistor 110 h and the otherfunctions as a drain of the transistor 110 h.

The conductive layer 263 b is electrically connected to the electrode191 that functions as a pixel electrode of a light-emitting elementthrough an opening provided in the insulating layer 214.

Hereinafter, the method for manufacturing the display device of thisembodiment will be specifically described with reference to FIGS. 9A to9D, FIGS. 10A to 10C, FIGS. 11A and 11B, and FIGS. 12A and 12B.

Note that thin films included in the display device (e.g., insulatingfilms, semiconductor films, or conductive films) can be formed by any ofa sputtering method, a chemical vapor deposition (CVD) method, a vacuumevaporation method, a pulsed laser deposition (PLD) method, an atomiclayer deposition (ALD) method, and the like. As the CVD method, aplasma-enhanced chemical vapor deposition (PECVD) method or a thermalCVD method may be used. As the thermal CVD method, for example, a metalorganic chemical vapor deposition (MOCVD) method may be used.

Alternatively, thin films included in the display device (e.g.,insulating films, semiconductor films, or conductive films) can beformed by a method such as spin coating, dipping, spray coating,ink-jetting, dispensing, screen printing, or offset printing, or with adoctor knife, a slit coater, a roll coater, a curtain coater, or a knifecoater.

When thin films included in the display device are processed, alithography method or the like can be used for the processing.Alternatively, island-shaped thin films may be formed by a filmformation method using a blocking mask. A nanoimprinting method, asandblasting method, a lift-off method, or the like may be used for theprocessing of thin films. Examples of a photolithography method includea method in which a resist mask is formed over a thin film to beprocessed, the thin film is processed by etching or the like, and theresist mask is removed, and a method in which a photosensitive thin filmis formed and exposed to light and developed to be processed into adesired shape.

In the case of using light in the lithography method, any of an i-line(light with a wavelength of 365 nm), a g-line (light with a wavelengthof 436 nm), and an h-line (light with a wavelength of 405 nm), orcombined light of any of them can be used for exposure. Alternatively,ultraviolet light, KrF laser light, ArF laser light, or the like can beused. Exposure may be performed by liquid immersion exposure technique.As the light for the exposure, extreme ultra-violet (EUV) light orX-rays may be used. Instead of the light for the exposure, an electronbeam can be used. It is preferable to use EUV, X-rays, or an electronbeam because extremely minute processing can be performed. Note that inthe case of performing exposure by scanning of a beam such as anelectron beam, a photomask is not needed.

For etching of thin films, a dry etching method, a wet etching method, asandblast method, or the like can be used.

<Example of Manufacturing Method of Display Device>

An example of a manufacturing method of the display device 300illustrated in FIG. 5 will be described below. The manufacturing methodwill be described with reference to FIGS. 9A to 9D, FIGS. 10A to 10C,FIGS. 11A and 11B, and FIGS. 12A and 12B, focusing on the displayportion 362 of the display device 300. Note that the transistor 203 isnot illustrated in FIGS. 9A to 9D, FIGS. 10A to 10C, FIGS. 11A and 11B,and FIGS. 12A and 12B.

First, the coloring layer 131 is formed over the substrate 361 (FIG.9A). The coloring layer 131 is formed using a photosensitive material,in which case the processing into an island shape can be performed by aphotolithography method or the like. Note that in the circuit 364 andthe like illustrated in FIG. 5, the light-blocking layer 132 is providedover the substrate 361.

Then, the insulating layer 121 is formed over the coloring layer 131 andthe light-blocking layer 132.

The insulating layer 121 preferably functions as a planarization layer.A resin such as acrylic or epoxy is suitably used for the insulatinglayer 121.

An inorganic insulating film may be used for the insulating layer 121.For example, an inorganic insulating film such as a silicon nitridefilm, a silicon oxynitride film, a silicon oxide film, a silicon nitrideoxide film, an aluminum oxide film, or an aluminum nitride film can beused for the insulating layer 121. Alternatively, a hafnium oxide film,an yttrium oxide film, a zirconium oxide film, a gallium oxide film, atantalum oxide film, a magnesium oxide film, a lanthanum oxide film, acerium oxide film, a neodymium oxide film, or the like may be used.Further alternatively, a stack including two or more of the aboveinsulating films may be used.

Next, the electrode 113 is formed. The electrode 113 can be formed inthe following manner: a conductive film is formed, a resist mask isformed, the conductive film is etched, and the resist mask is removed.The electrode 113 is formed using a conductive material that transmitsvisible light.

After that, the insulating layer 117 is formed over the electrode 113.An organic insulating film is preferably used for the insulating layer117.

Subsequently, the alignment film 133 b is formed over the electrode 113and the insulating layer 117 (FIG. 9A). The alignment film 133 b can beformed in the following manner: a thin film is formed using a resin orthe like, and then, rubbing treatment is performed.

Note that steps illustrated in FIGS. 9B to 9D, FIGS. 10A to 10C, FIGS.11A and 11B, and FIG. 12A are performed independently of the stepsdescribed with reference to FIG. 9A.

First, a separation layer 62 is formed over a formation substrate 61,and an insulating layer 63 is formed over the separation layer 62 (FIG.9B).

In this step, a material is selected that would cause separation at theinterface between the formation substrate 61 and the separation layer62, the interface between the separation layer 62 and the insulatinglayer 63, or in the separation layer 62 when the formation substrate 61is peeled. In this embodiment, an example in which separation occurs atthe interface between the insulating layer 63 and the separation layer62 is described; however, one embodiment of the present invention is notlimited to such an example and depends on a material used for theseparation layer 62 or the insulating layer 63.

The formation substrate 61 has stiffness high enough for easy transferand has resistance to heat applied in the manufacturing process.Examples of a material that can be used for the formation substrate 61include glass, quartz, ceramics, sapphire, a resin, a semiconductor, ametal, and an alloy. Examples of the glass include alkali-free glass,barium borosilicate glass, and aluminoborosilicate glass.

The separation layer 62 can be formed using an organic material or aninorganic material.

Examples of an inorganic material that can be used for the separationlayer 62 include a metal containing an element selected from tungsten,molybdenum, titanium, tantalum, niobium, nickel, cobalt, zirconium,zinc, ruthenium, rhodium, palladium, osmium, iridium, and silicon; analloy containing any of the above elements; and a compound containingany of the above elements. A crystal structure of a layer containingsilicon may be amorphous, microcrystal, or polycrystal.

In the case of using an inorganic material, the thickness of theseparation layer 62 is greater than or equal to 1 nm and less than orequal to 1000 nm, preferably greater than or equal to 10 nm and lessthan or equal to 200 nm, and further preferably greater than or equal to10 nm and less than or equal to 100 nm.

In the case of using an inorganic material, the separation layer 62 canbe formed by a sputtering method, a CVD method, an ALD method, or anevaporation method, for example.

Examples of an organic material that can be used for the separationlayer 62 include a polyimide resin, an acrylic resin, an epoxy resin, apolyamide resin, a polyimide-amide resin, a siloxane resin, abenzocyclobutene-based resin, and a phenol resin.

In the case of using an organic material, the thickness of theseparation layer 62 is preferably greater than or equal to 0.01 μm andless than 10 μm, further preferably greater than or equal to 0.1 μm andless than or equal to 3 μm, and still further preferably greater than orequal to 0.5 μm and less than or equal to 1 μm. The separation layer 62whose thickness is within the above range can lead to a reduction inmanufacturing cost. The thickness of the separation layer 62 is notnecessarily within the above range and may be greater than or equal to10 μm: for example, greater than or equal to 10 μm and less than orequal to 200 μm.

In the case of using an organic material, the separation layer 62 can beformed by spin coating, dipping, spray coating, ink-jetting, dispensing,screen printing, or offset printing, or with a doctor knife, a slitcoater, a roll coater, a curtain coater, or a knife coater, for example.

An inorganic insulating film is preferably formed using the insulatinglayer 63. For example, an inorganic insulating film such as a siliconnitride film, a silicon oxynitride film, a silicon oxide film, a siliconnitride oxide film, an aluminum oxide film, or an aluminum nitride filmcan be used for the insulating layer 63. Alternatively, a hafnium oxidefilm, an yttrium oxide film, a zirconium oxide film, a gallium oxidefilm, a tantalum oxide film, a magnesium oxide film, a lanthanum oxidefilm, a cerium oxide film, a neodymium oxide film, or the like may beused. Further alternatively, a stack including two or more of the aboveinsulating films may be used.

For example, a stacked-layer structure of a layer containing ahigh-melting-point metal material such as tungsten and a layercontaining an oxide of the metal material may be used for the separationlayer 62, and a stacked-layer structure of a plurality of inorganicinsulating films containing silicon nitride, silicon oxynitride, siliconnitride oxide, or the like may be used for the insulating layer 63. Whena high-melting-point metal material is used for the separation layer 62,layers formed after the separation layer 62 can be formed at highertemperatures; thus, impurity concentration can be reduced and a highlyreliable display device can be fabricated. A step for removing a layerunnecessary for the display device (e.g., the separation layer 62 or theinsulating layer 63) may be performed after the peeling. The separationlayer 62 or the insulating layer 63 is not necessarily removed and maybe used as a component of the display device.

Next, the electrode 311 a is formed over the insulating layer 63, andthe electrode 311 b is formed over the electrode 311 a (FIG. 9C). Theelectrode 311 b includes the opening 451 over the electrode 311 a. Eachof the electrodes 311 a and 311 b can be formed in the following manner:a conductive film is formed, a resist mask is formed, the conductivefilm is etched, and the resist mask is removed. The electrode 311 a isformed using a conductive material that transmits visible light. Theelectrode 311 b is formed using a conductive material that reflectsvisible light.

After that, the insulating layer 220 is formed (FIG. 9D). Then, anopening that reaches the electrode 311 b is formed in the insulatinglayer 220.

The insulating layer 220 can be used as a barrier layer that preventsdiffusion of impurities contained in the separation layer 62 into thetransistor and the display element formed later. In the case of using anorganic material for the separation layer 62, the insulating layer 220preferably prevents diffusion of moisture or the like contained in theseparation layer 62 into the transistor and the display element when theseparation layer 62 is heated. Thus, the insulating layer 220 preferablyhas a high barrier property.

The insulating layer 220 can be formed using the inorganic insulatingfilm, the resin, or the like that can be used for the insulating layer121.

Next, the transistor 205 and the transistor 206 are formed over theinsulating layer 220.

There is no particular limitation on a semiconductor material used forthe semiconductor layer of the transistor, and for example, a Group 14element, a compound semiconductor, or an oxide semiconductor can beused. Typically, a semiconductor containing silicon, a semiconductorcontaining gallium arsenide, an oxide semiconductor containing indium,or the like can be used.

Described here is the case where a bottom-gate transistor including anoxide semiconductor layer as the semiconductor layer 231 is fabricatedas the transistor 206. The transistor 205 includes the conductive layer223 and the insulating layer 212 in addition to the components of thetransistor 206, and has two gates.

An oxide semiconductor is preferably used for the semiconductor layer ofthe transistor. The use of a semiconductor material having a wider bandgap and a lower carrier density than silicon can reduce off-statecurrent of the transistor.

Specifically, first, the conductive layer 221 a and the conductive layer221 b are formed over the insulating layer 220. The conductive layer 221a and the conductive layer 221 b can be formed in the following manner:a conductive film is formed, a resist mask is formed, the conductivefilm is etched, and the resist mask is removed. At this time, theconductive layer 221 b and the electrode 311 b are connected to eachother through an opening in the insulating layer 220.

Next, the insulating layer 211 is formed.

For the insulating layer 221, for example, an inorganic insulating filmsuch as a silicon nitride film, a silicon oxynitride film, a siliconoxide film, a silicon nitride oxide film, an aluminum oxide film, or analuminum nitride film can be used. Alternatively, a hafnium oxide film,an yttrium oxide film, a zirconium oxide film, a gallium oxide film, atantalum oxide film, a magnesium oxide film, a lanthanum oxide film, acerium oxide film, a neodymium oxide film, or the like may be used.Further alternatively, a stack including two or more of the aboveinsulating films may be used.

An inorganic insulating film is preferably formed at high temperaturesbecause the film can have higher density and a higher barrier propertyas the deposition temperature becomes higher. The substrate temperatureduring the deposition of the inorganic insulating film is preferablyhigher than or equal to room temperature (25° C.) and lower than orequal to 350° C., and further preferably higher than or equal to 100° C.and lower than or equal to 300° C.

Then, the semiconductor layer 231 is formed. In this embodiment, anoxide semiconductor layer is formed as the semiconductor layer 231. Theoxide semiconductor layer can be formed in the following manner: anoxide semiconductor film is formed, a resist mask is formed, the oxidesemiconductor film is etched, and the resist mask is removed.

The substrate temperature during the deposition of the oxidesemiconductor film is preferably lower than or equal to 350° C., furtherpreferably higher than or equal to room temperature and lower than orequal to 200° C., and still further preferably higher than or equal toroom temperature and lower than or equal to 130° C.

The oxide semiconductor film can be formed using one or both of an inertgas and an oxygen gas. Note that there is no particular limitation onthe percentage of oxygen flow rate (partial pressure of oxygen) at thetime of forming the oxide semiconductor film. To fabricate a transistorhaving high field-effect mobility, however, the percentage of oxygenflow rate (partial pressure of oxygen) at the time of forming the oxidesemiconductor film is preferably higher than or equal to 0% and lowerthan or equal to 30%, further preferably higher than or equal to 5% andlower than or equal to 30%, and still further preferably higher than orequal to 7% and lower than or equal to 15%.

The oxide semiconductor film preferably contains at least indium orzinc. It is particularly preferable to contain indium and zinc.

The energy gap of the oxide semiconductor is preferably 2 eV or more,further preferably 2.5 eV or more, and still further preferably 3 eV ormore. The use of such an oxide semiconductor having a wide energy gapleads to a reduction in off-state current of a transistor.

The oxide semiconductor film can be formed by a sputtering method.Alternatively, a PLD method, a PECVD method, a thermal CVD method, anALD method, a vacuum evaporation method, or the like may be used.

Note that an example of an oxide semiconductor will be described inEmbodiment 5.

Next, the conductive layer 222 a and the conductive layer 222 b areformed. The conductive layer 222 a and the conductive layer 222 b can beformed in the following manner: a conductive film is formed, a resistmask is formed, the conductive film is etched, and the resist mask isremoved. Each of the conductive layers 222 a and 222 b is connected tothe semiconductor layer 231. Here, the conductive layer 222 a includedin the transistor 206 is electrically connected to the conductive layer221 b. As a result, the electrode 311 b and the conductive layer 222 acan be electrically connected to each other at the connection portion207.

Note that during the processing of the conductive layer 222 a and theconductive layer 222 b, the semiconductor layer 231 might be partlyetched to be thin in a region not covered by the resist mask.

In the above manner, the transistor 206 can be fabricated (FIG. 9D). Inthe transistor 206, part of the conductive layer 221 a functions as agate, part of the insulating layer 211 functions as a gate insulatinglayer, and the conductive layer 222 a and the conductive layer 222 bfunction as a source and a drain.

Next, the insulating layer 212 that covers the transistor 206 is formed,and the conductive layer 223 is formed over the insulating layer 212.

The insulating layer 212 can be formed in a manner similar to that ofthe insulating layer 211.

The conductive layer 223 included in the transistor 205 can be formed inthe following manner: a conductive film is formed, a resist mask isformed, the conductive film is etched, and the resist mask is removed.

In the above manner, the transistor 205 can be fabricated (FIG. 9D). Inthe transistor 205, part of the conductive layer 221 a and part of theconductive layer 223 function as gates, part of the insulating layer 211and part of the insulating layer 212 function as gate insulating layers,and the conductive layer 222 a and the conductive layer 222 b functionas a source and a drain.

Next, the insulating layer 213 is formed (FIG. 9D). The insulating layer213 can be formed in a manner similar to that of the insulating layer211.

It is preferable to use an oxide insulating film formed in an atmospherecontaining oxygen, such as a silicon oxide film or a silicon oxynitridefilm, for the insulating layer 212. An insulating film with low oxygendiffusibility and oxygen permeability, such as a silicon nitride film,is preferably stacked as the insulating layer 213 over the silicon oxidefilm or the silicon oxynitride film. The oxide insulating film formed inan atmosphere containing oxygen can easily release a large amount ofoxygen by heating. When a stack including such an oxide insulating filmthat releases oxygen and an insulating film with low oxygendiffusibility and oxygen permeability is heated, oxygen can be suppliedto the oxide semiconductor layer. As a result, oxygen vacancies in theoxide semiconductor layer can be filled and defects at the interfacebetween the oxide semiconductor layer and the insulating layer 212 canbe repaired, leading to a reduction in defect levels. Accordingly, anextremely highly reliable display device can be fabricated.

Next, the coloring layer 134 is formed over the insulating layer 213(FIG. 9D), and then, the insulating layer 214 is formed (FIG. 10A). Thecoloring layer 134 is positioned so as to overlap with the opening 451in the electrode 311 b.

The coloring layer 134 can be formed in a manner similar to that of thecoloring layer 131. The display element is formed on the insulatinglayer 214 in a later step; thus, the insulating layer 214 preferablyfunctions as a planarization layer. For the insulating layer 214, thedescription of the resin or the inorganic insulating film that can beused for the insulating layer 121 can be referred to.

After that, an opening that reaches the conductive layer 222 a includedin the transistor 205 is formed in the insulating layer 212, theinsulating layer 213, and the insulating layer 214.

Subsequently, the electrode 191 is formed (FIG. 10A). The electrode 191can be formed in the following manner: a conductive film is formed, aresist mask is formed, the conductive film is etched, and the resistmask is removed. Here, the conductive layer 222 a included in thetransistor 205 and the electrode 191 are connected to each other. Theelectrode 191 is formed using a conductive material that transmitsvisible light.

Then, the insulating layer 216 that covers the end portion of theelectrode 191 is formed (FIG. 10B). For the insulating layer 216, thedescription of the resin or the inorganic insulating film that can beused for the insulating layer 121 can be referred to. The insulatinglayer 216 includes an opening in a region overlapping with the electrode191.

Next, the EL layer 192 and the electrode 193 are formed (FIG. 10B). Partof the electrode 193 functions as the common electrode of thelight-emitting element 170. The electrode 193 is formed using aconductive material that reflects visible light.

The EL layer 192 can be formed by an evaporation method, a coatingmethod, a printing method, a discharge method, or the like. In the casewhere the EL layer 192 is formed for each individual pixel, anevaporation method using a shadow mask such as a metal mask, an ink-jetmethod, or the like can be used. In the case of sharing the EL layer 192by some pixels, an evaporation method not using a metal mask can beused.

Either a low molecular compound or a high molecular compound can be usedfor the EL layer 192, and an inorganic compound may also be included.

Steps after the formation of the EL layer 192 are performed such thattemperatures higher than the heat resistant temperature of the EL layer192 are not applied to the EL layer 192. The electrode 193 can be formedby an evaporation method, a sputtering method, or the like.

In the above manner, the light-emitting element 170 can be formed (FIG.10B). In the light-emitting element 170, the electrode 191 part of whichfunctions as the pixel electrode, the EL layer 192, and the electrode193 part of which functions as the common electrode are stacked. Thelight-emitting element 170 is formed such that the light-emitting regionoverlaps with the coloring layer 134 and the opening 451 in theelectrode 311 b.

Although an example where a bottom-emission light-emitting element isformed as the light-emitting element 170 is described here, oneembodiment of the present invention is not limited thereto.

The light-emitting element may be a top emission, bottom emission, ordual emission light-emitting element. A conductive film that transmitsvisible light is used as the electrode through which light is extracted.A conductive film that reflects visible light is preferably used as theelectrode through which light is not extracted.

Next, the insulating layer 194 is formed so as to cover the electrode193 (FIG. 10B). The insulating layer 194 functions as a protective layerthat prevents diffusion of impurities such as water into thelight-emitting element 170. The light-emitting element 170 is sealedwith the insulating layer 194. After the electrode 193 is formed, theinsulating layer 194 is preferably formed without exposure to the air.

The inorganic insulating film that can be used for the insulating layer121 can be used for the insulating layer 194, for example. It isparticularly preferable that the insulating layer 194 include aninorganic insulating film with a high barrier property. A stackincluding an inorganic insulating film and an organic insulating filmcan also be used.

The insulating layer 194 is preferably formed at substrate temperaturelower than or equal to the heat resistant temperature of the EL layer192. The insulating layer 194 can be formed by an ALD method, asputtering method, or the like. An ALD method and a sputtering methodare preferable because a film can be formed at low temperatures. An ALDmethod is preferable because the coverage of the insulating layer 194 isimproved.

Then, the substrate 351 is bonded to a surface of the insulating layer194 with the adhesive layer 142 (FIG. 10C).

As the adhesive layer 142, any of a variety of curable adhesives such asa reactive curable adhesive, a thermosetting adhesive, an anaerobicadhesive, and a photocurable adhesive such as an ultraviolet curableadhesive can be used. Alternatively, an adhesive sheet or the like maybe used.

For the substrate 351, a polyester resin such as polyethyleneterephthalate (PET) or polyethylene naphthalate (PEN), apolyacrylonitrile resin, an acrylic resin, a polyimide resin, apolymethyl methacrylate resin, a polycarbonate (PC) resin, apolyethersulfone (PES) resin, a polyamide resin (e.g., nylon or aramid),a polysiloxane resin, a cycloolefin resin, a polystyrene resin, apolyamide-imide resin, a polyurethane resin, a polyvinyl chloride resin,a polyvinylidene chloride resin, a polypropylene resin, apolytetrafluoroethylene (PTFE) resin, an ABS resin, or cellulosenanofiber can be used, for example. Any of a variety of materials suchas glass, quartz, a resin, a metal, an alloy, and a semiconductor can beused for the substrate 351. The substrate 351 formed using any of avariety of materials such as glass, quartz, a resin, a metal, an alloy,and a semiconductor may be thin enough to be flexible.

After that, the formation substrate 61 is peeled (FIG. 11A).

The position of the separation surface depends on the materials, theformation methods, and the like of the insulating layer 63, theseparation layer 62, the formation substrate 61, and the like.

FIG. 11A illustrates an example where the separation occurs at theinterface between the separation layer 62 and the insulating layer 63.By the separation, the insulating layer 63 is exposed.

Before the separation, a separation trigger may be formed in theseparation layer 62. For example, part of or the entire separation layer62 may be irradiated with laser light, in which case the separationlayer 62 can be embrittled or the adhesion between the separation layer62 and the insulating layer 63 (or the formation substrate 61) can bereduced.

The formation substrate 61 can be peeled by applying a perpendiculartensile force to the separation layer 62, for example. Specifically, theformation substrate 61 can be peeled by pulling up the substrate 351 bypart of its suction-attached top surface.

The separation trigger may be formed by inserting a sharp instrumentsuch as a knife between the separation layer 62 and the insulating layer63 (or the formation substrate 61). Alternatively, the separationtrigger may be formed by cutting the separation layer 62 from thesubstrate 351 side with a sharp instrument.

Next, the insulating layer 63 is removed. The insulating layer 63 can beremoved by a dry etching method, for example. Accordingly, the electrode311 a is exposed (FIG. 11B).

Subsequently, the alignment film 133 a is formed on the exposed surfaceof the electrode 311 a (FIG. 12A). The alignment film 133 a can beformed in the following manner: a thin film is formed using a resin orthe like, and then, rubbing treatment is performed.

Then, the substrate 361 obtained from the steps described using FIG. 9Aand the substrate 351 obtained from the steps up to the step illustratedin FIG. 12A are bonded to each other with the liquid crystal layer 112provided therebetween (FIG. 12B). Although not illustrated in FIG. 12B,the substrate 351 and the substrate 361 are bonded to each other withthe adhesive layer 141 as illustrated in FIG. 5 and other drawings. Formaterials of the adhesive layer 141, the description of the materialsthat can be used for the adhesive layer 142 can be referred to.

In the liquid crystal element 180 illustrated in FIG. 12B, the electrode311 a (and the electrode 311 b) part of which functions as the pixelelectrode, the liquid crystal layer 112, and the electrode 113 part ofwhich functions as the common electrode are stacked. The liquid crystalelement 180 is formed so as to overlap with the coloring layer 131.

Through the above steps, the display device 300 can be fabricated. Notethat the polarizing plate 135 is placed on the outer surface of thesubstrate 361. Furthermore, the FPC 372 is connected to the displaydevice via the connection layer 242, as illustrated in FIG. 5 and otherdrawings.

The display device of this embodiment includes two types of displayelements as described above; thus, switching between a plurality ofdisplay modes is possible. Accordingly, the display device can have highvisibility regardless of the ambient brightness, leading to highconvenience.

In the display device of this embodiment, the distance between the layerincluded in the first display element that has a function of reflectingvisible light and the second display element can be shortened; thus,high viewing angle characteristics of the display device and a highaperture ratio of the first display element can be both achieved. Inaddition, the total aperture ratio of the first display element and thesecond display element can be increased.

This embodiment can be combined with any other embodiment asappropriate. In the case where a plurality of structure examples aredescribed in one embodiment in this specification, some of the structureexamples can be combined as appropriate.

Embodiment 2

In this embodiment, the display device of one embodiment of the presentinvention will be described with reference to FIG. 1, FIG. 4, FIGS. 13Aand 13B, FIG. 14, FIGS. 15A and 15B, FIG. 16, FIG. 17, and FIGS. 18A and18B.

As in Embodiment 1, a display device including a first display elementthat reflects visible light and a second display element that emitsvisible light will be described in this embodiment.

First, the display device 10 illustrated in FIG. 1 is described as anexample.

The display device of this embodiment has a wide viewing angle; thus,even when the display device is seen from an oblique direction, contrastis less likely to be reduced and chromaticity is less likely to change.Thus, high visibility can be obtained not only in the case of seeing thedisplay device from the front, but also in the case of seeing thedisplay device from an oblique direction. For example, even when aplurality of viewers see the display device of this embodiment fromvarious angles at the same time, information displayed on the displaydevice can be recognized by the viewers. The display device of thisembodiment is suitable for display portions of portable electronicdevices, display portions of personal electronic devices, and largedisplay portions of television devices, digital signage (electronicsignboards), public information displays (PIDs), and the like.

Specifically, when a viewer sees the display device of this embodimentfrom a direction inclined by 85° from a direction perpendicular to thedisplay surface of the display device, the viewer can see 10% or more ofthe area of the light-emitting region of the light-emitting element 170.When a viewer can see 10% or more of the area of the light-emittingregion of the light-emitting element 170, information displayed on thedisplay device can be recognized enough. The area of the light-emittingregion of the light-emitting element 170 that can be seen from thedirection inclined by 85° is preferably as large as possible becauseinformation displayed on the display device can be easily recognized.

When a viewer sees the display device of this embodiment from adirection inclined by 30° from the direction perpendicular to thedisplay surface of the display device, the viewer can see 100% of thearea of the light-emitting region of the light-emitting element 170. Inthat case, the luminance of an image that a viewer sees is equivalent tothat in the case of seeing from the direction perpendicular to thedisplay surface (θ=0°). This means that an image can be seen with thesame quality even when a user sees the display device from the directionslightly inclined with respect to the display surface.

As described above, a viewer can recognize information displayed on thedisplay device of this embodiment from an extremely wide range ofviewing position.

Next, examples of conditions of the display device for obtaining such astructure will be described.

FIG. 13A illustrates light emission from the light-emitting element 170that can be seen by a viewer from the direction perpendicular to thedisplay surface (θ=0°) and light emission that can be seen from adirection inclined by 85° from the direction perpendicular to thedisplay surface (θ=85°). FIG. 13B illustrates light emission from thelight-emitting element 170 that can be seen by a viewer from thedirection perpendicular to the display surface (θ=0°) and light emissionthat can be seen from a direction inclined by 30° from the directionperpendicular to the display surface (θ=30°). FIGS. 13A and 13Billustrate only the electrode 193 of the light-emitting element 170 foreasy description.

The description below is made using a first plane 51 including a planeof the electrode 311 on the viewer's side in the display region of theliquid crystal element 180 and a second plane 52 including a plane ofthe electrode 193 on the viewer's side in the display region (alsoreferred to as a light-emitting region) of the light-emitting element170. Note that the electrode 311 is a layer having a function ofreflecting visible light, which is included in the liquid crystalelement 180. The electrode 193 is a layer having a function ofreflecting visible light, which is included in the light-emittingelement 170. The electrode 193 can reflect light emitted from the ELlayer 192. Thus, a distance D, which will be described later, can bedetermined with reference to the electrode 193. Note that the displayregion of the display element is a region contributing to displaying animage in the display element.

The description below is made on the assumption that there is no layerthat blocks light emission from the light-emitting element on a sidecloser to a viewer than the electrode 311. It is also assumed that totalreflection of light emission from the light-emitting element does notoccur on the side closer to a viewer than the electrode 311.Accordingly, a viewer can see all of light that is emitted from thelight-emitting element and is extracted through an opening in theelectrode 311.

In FIGS. 13A and 13B, a length A represents the length between the endportion of the electrode 311 and the foot of the perpendicular drawnfrom the end portion of the electrode 193 (or from an end portion of thedisplay region of the light-emitting element 170) to the first plane 51.The length A is greater than or equal to 0. The distance D representsthe shortest distance between the first plane 51 and the second plane52. A refractive index N represents the refractive index between thefirst plane 51 and the second plane 52 in a region overlapping with theopening in the electrode 311. The refractive index N is greater than orequal to 1. The refractive index of the outside of the display deviceis 1. A length L represents the width of the electrode 193. The length Lcan also be referred to as the width of the display region of thelight-emitting element 170. Each of an angle θ₁ and an angle θ₂represents an angle formed by a perpendicular from the second plane 52to the first plane 51 and incident light from the light-emitting element170 to the first plane 51.

In the case of seeing the display device from the direction where θ is0°, a viewer sees light that is emitted perpendicular to the displaysurface from the light-emitting element, as illustrated in FIG. 13A.Furthermore, in the case of seeing the display device from the directionwhere θ is 85°, a viewer sees light that enters the first plane 51 atthe angle θ₁ from the light-emitting element.

As illustrated in FIG. 13A, when the display device is seen from thedirection inclined from the direction perpendicular to the displaysurface, the light-emitting region of the light-emitting element 170 ispartially blocked from view by the electrode 311, in some cases. Whenlight emitted from the light-emitting element 170 is partially blockedby the electrode 311, the luminance of an image that a viewer sees islower than that in the case of seeing from the direction perpendicularto the display surface.

The display device of this embodiment preferably satisfies Formula (1)and Formula (2).

$\begin{matrix}{\lbrack {{Formulae}\mspace{14mu} 4} \rbrack \mspace{616mu}} & \; \\{{D\; \tan \; \theta_{1}} \leq {{\frac{9}{10}L} + A}} & (1) \\{\frac{\sin \; \theta_{1}}{\sin \; 85{^\circ}} = \frac{1}{N}} & (2)\end{matrix}$

If Formula (1) and Formula (2) are satisfied, a viewer can see 10% ormore of the area of the light-emitting region of the light-emittingelement 170 when seeing from the direction where θ is 85°. Thus,information displayed on the display device can be recognized even whenthe display device is seen from the direction greatly inclined withrespect to the display device.

FIG. 13A illustrates an example where D tan θ₁=9L/10+A is satisfied anda viewer can see 50% or more of the area of the light-emitting region ofthe light-emitting element 170 from the direction where θ is 85°.

In the case of seeing from the direction where θ is 0°, a viewer seeslight that is emitted perpendicular to the display surface from thelight-emitting element, as illustrated in FIG. 13B. Furthermore, in thecase of seeing from the direction where θ is 30°, a viewer sees lightthat enters the first plane 51 at the angle θ₂ from the light-emittingelement.

The display device of this embodiment preferably satisfies Formula (3)and Formula (4).

$\begin{matrix}{\lbrack {{Formulae}\mspace{14mu} 5} \rbrack \mspace{616mu}} & \; \\{{D\; \tan \; \theta_{2}} \leq A} & (3) \\{\frac{\sin \; \theta_{2}}{\sin \; 30{^\circ}} = \frac{1}{N}} & (4)\end{matrix}$

If Formula (3) and Formula (4) are satisfied, a viewer can see 100% ofthe area of the light-emitting region of the light-emitting element 170when seeing from the direction where θ is 30°. Thus, an image can beseen with the same quality even when a user sees the display device froma direction slightly inclined with respect to the display surface.

FIG. 13B illustrates an example where D tan θ₂<A is satisfied.

Note that layers on a side closer to a viewer than the electrode 311 inFIG. 1 (e.g., the substrate 361 and the electrode 113) are notillustrated in FIGS. 13A and 13B.

In FIG. 14, the description is made on the assumption that a singlelayer having a refractive index N_(b) and a thickness D_(b) is on a sidecloser to a viewer than the electrode 311.

In the case of seeing from the direction where θ is 0°, a viewer seeslight that is emitted perpendicular to the display surface from thelight-emitting element, as illustrated in FIG. 14. Furthermore, in thecase of seeing from the direction where θ is 85°, a viewer sees lightthat enters the first plane 51 at the angle θ₁ from the light-emittingelement.

Since N sin θ₁=N_(b) sin θ_(b) and N_(b) sin θ₁=sin 85° are satisfied inaccordance with the law of refraction (also referred to as Snell's law),N sin θ₁=sin 85° is satisfied.

As described above, the refractive index N_(b) and the thickness D_(b)of the layer on a side closer to a viewer than the electrode 311 do notaffect the relationship between the direction from which the viewer seesand the angle θ₁. This means that there is no difference in the area ofthe light-emitting region of the light-emitting element 170 seen by aviewer, between the case of assuming a layer on a side closer to theviewer than the electrode 311 and the case of assuming no such a layer.For this reason, layers on a side closer to a viewer than the electrode311 are not illustrated in FIGS. 13A and 13B.

In Formula (2) and Formula (4), the refractive index between the firstplane 51 and the second plane 52 in the region overlapping with theopening in the electrode 311 is represented by N. In the case wherethere is a layer having a single-layer structure between the first plane51 and the second plane 52 in the region overlapping with the opening inthe electrode 311, the refractive index of the layer can be representedby N.

In FIG. 1, in contrast, the insulating layer 220 and the insulatinglayer 214 are provided between the first plane 51 and the second plane52 in the region overlapping with the opening in the electrode 311. Inthe case where there is a stacked-layer structure between the firstplane 51 and the second plane 52 in the region overlapping with theopening in the electrode 311 as in FIG. 1, the refractive index N can beobtained using the refractive indices and the thicknesses of layersincluded in the stacked-layer structure.

FIG. 15A illustrates an example where a stacked-layer structure of alayers (a is an integer greater than or equal to 2) is provided betweenthe first plane 51 and the second plane 52 in the region overlappingwith the opening in the electrode 311. In FIG. 15A, the layer closest tothe electrode 193 is illustrated as a first layer and the layer closestto the electrode 311 is illustrated as an a-th layer; the order may bereversed. The sum of thicknesses D_(x) (x is an integer greater than orequal to 1 and less than or equal to a) of the a layers corresponds tothe distance D. The sum of the products of a refractive index N_(x) andthe thickness D_(x) of an x-th layer in all layers corresponds to theproduct of the refractive index N and the distance D. Thus, therefractive index N satisfies Formula (5).

$\begin{matrix}{\lbrack {{Formula}\mspace{14mu} 6} \rbrack \mspace{625mu}} & \; \\{N = \frac{\sum\limits_{x = 1}^{a}\; {N_{x}D_{x}}}{D}} & (5)\end{matrix}$

Note that the refractive index N is not necessarily obtained fromFormula (5).

Formula (5) indicates that a thick layer greatly affects the value ofthe refractive index N. Thus, the value of the refractive index of thethickest layer in the stacked-layer structure may be used as therefractive index N. In many cases, an organic insulating film is formedthicker than an inorganic insulating film, for example. Accordingly, thevalue of the refractive index of a layer formed using an organicinsulating film in the stacked-layer structure of a layers may be usedas the refractive index N.

A display device having a wide viewing angle can be fabricated also inthe case where Formulae (6) to (9) described below are satisfied.

Hereinafter, an example where a layer with a refractive index N₁ and athickness D₁ and a layer with a refractive index N₂ and a thickness D₂are provided between the first plane 51 and the second plane 52 in theregion overlapping with the opening in the electrode 311 is described.Note that in the case where the refractive index N₁ and the refractiveindex N₂ are different from each other, light emitted from thelight-emitting element is refracted at the interface between the twolayers.

FIG. 15B illustrates light emission from the light-emitting element 170that can be seen by a viewer from the direction perpendicular to thedisplay surface (θ=0°) and light emission that can be seen from thedirection inclined by 85° from the direction perpendicular to thedisplay surface (θ=85°). FIG. 15B illustrates only the electrode 193 ofthe light-emitting element 170 for easy description.

In FIG. 15B, the length A represents the length between the end portionof the electrode 311 and the foot of the perpendicular drawn from theend portion of the electrode 193 (or from the end portion of the displayregion of the light-emitting element 170) to the first plane 51. Thelength A is greater than or equal to 0. The refractive index of theoutside of the display device is 1. The length L represents the width ofthe electrode 193. The length L can also be referred to as the width ofthe display region of the light-emitting element 170. The angle θ₁represents an angle formed by the perpendicular from the second plane 52to the first plane 51 and incident light from the light-emitting element170 to the layer with the refractive index N₂. The angle θ₂ representsan angle formed by the perpendicular from the second plane 52 to thefirst plane 51 and incident light from the light-emitting element 170 tothe first plane 51.

In the case of seeing the display device from the direction where θ is0°, a viewer sees light that is emitted perpendicular to the displaysurface from the light-emitting element, as illustrated in FIG. 15B.Furthermore, in the case of seeing the display device from the directionwhere θ is 85°, a viewer sees light that enters the first plane 51 atthe angle θ₂ from the light-emitting element.

As illustrated in FIG. 15B, when the display device is seen from thedirection inclined from the direction perpendicular to the displaysurface, the light-emitting region of the light-emitting element 170 ispartially blocked from view by the electrode 311, in some cases. Whenlight emitted from the light-emitting element 170 is partially blockedby the electrode 311, the luminance of an image that a viewer sees islower than that in the case of seeing from the direction perpendicularto the display surface.

The display device illustrated in FIG. 15B preferably satisfies Formula(6A), Formula (7A), and Formula (8A).

$\begin{matrix}{\lbrack {{Formulae}\mspace{14mu} 7} \rbrack \mspace{596mu}} & \; \\{{{D_{1}\; \tan \; \theta_{1}} + {D_{2}\tan \; \theta_{2}}} \leq {{\frac{9}{10}L} + A}} & ( {6A} ) \\{\frac{\sin \; \theta_{1}}{\sin \; 85{^\circ}} = \frac{1}{N_{1}}} & ( {7A} ) \\{\frac{\sin \; \theta_{2}}{\sin \; 85{^\circ}} = \frac{1}{N_{2}}} & ( {8A} )\end{matrix}$

If Formula (6A), Formula (7A), and Formula (8A) are satisfied, a viewercan see 10% or more of the area of the light-emitting region of thelight-emitting element 170 when seeing from the direction where θ is85°. Thus, information displayed on the display device can be recognizedeven when the display device is seen from the direction greatly inclinedwith respect to the display device.

FIG. 15B illustrates an example where D₁ tan θ₁+D₂ tan θ₂=L/2+A issatisfied and a viewer can see 10% or more and less than 50% of the areaof the light-emitting region of the light-emitting element 170 from thedirection where θ is 85°.

Accordingly, in the case where the display device of this embodimentincludes the stacked-layer structure of a layers between the first plane51 and the second plane 52 in the region overlapping with the opening inthe electrode 311, it is preferable to satisfy Formula (6) and Formula(7).

$\begin{matrix}{\lbrack {{Formulae}\mspace{14mu} 8} \rbrack \mspace{616mu}} & \; \\{{\sum\limits_{x = 1}^{a}\; {{D\;}_{x}\tan \; \theta_{x}}} \leq {{\frac{9}{10}L} + A}} & (6) \\{\frac{\sin \; \theta_{x}}{\sin \; 85{^\circ}} = \frac{1}{N_{x}}} & (7)\end{matrix}$

In Formula (6) and Formula (7), a is an integer greater than or equal to2, x is an integer greater than or equal to 1 and less than or equal toa, D_(x) represents the thickness of the x-th layer in the stacked-layerstructure, N_(x) representing the refractive index of the x-th layer inthe stacked-layer structure is greater than or equal to 1, and θ_(x)represents an angle formed by the perpendicular from the second plane 52to the first plane 51 and refracted light of light emitted by thelight-emitting element 170 from an (x−1)-th layer to the x-th layer.

If Formula (6) and Formula (7) are satisfied, a viewer can see 10% ormore of the area of the light-emitting region of the light-emittingelement 170 when seeing from the direction where θ is 85°. Thus,information displayed on the display device can be recognized even whenthe display device is seen from the direction greatly inclined withrespect to the display device.

In the case where the display device of this embodiment includes thestacked-layer structure of a layers between the first plane 51 and thesecond plane 52 in the region overlapping with the opening in theelectrode 311, it is also preferable to satisfy Formula (8) and Formula(9).

$\begin{matrix}{\lbrack {{Formulae}\mspace{14mu} 9} \rbrack \mspace{616mu}} & \; \\{{\sum\limits_{y = 1}^{a}\; {{D\;}_{y}\tan \; \theta_{y}}} \leq A} & (8) \\{\frac{\sin \; \theta_{y}}{\sin \; 30{^\circ}} = \frac{1}{N_{y}}} & (9)\end{matrix}$

In Formula (8) and Formula (9), a is an integer greater than or equal to2, y is an integer greater than or equal to 1 and less than or equal toa, D_(y) represents the thickness of a y-th layer in the stacked-layerstructure, N_(y) representing the refractive index of the y-th layer inthe stacked-layer structure is greater than or equal to 1, and θ_(y)represents an angle formed by the perpendicular from the second plane 52to the first plane 51 and refracted light of light emitted by thelight-emitting element 170 from an (y−1)-th layer to the y-th layer.

If Formula (8) and Formula (9) are satisfied, a viewer can see 100% ofthe area of the light-emitting region of the light-emitting element 170when seeing from the direction where θ is 30°. Thus, an image can beseen with the same quality even when a user sees the display device froma direction slightly inclined with respect to the display surface.

As described above, the display device of this embodiment has a wideviewing angle; thus, even when the display device is seen from anoblique direction, contrast is less likely to be reduced andchromaticity is less likely to change. Thus, high visibility can beobtained not only in the case of seeing the display device from thefront, but also in the case of seeing the display device from an obliquedirection.

Next, structure examples of the display device of this embodiment willbe described with reference to FIG. 4, FIG. 16, FIG. 17, and FIGS. 18Aand 18B.

FIG. 4 is a schematic perspective view of the display device of thisembodiment. The details of the display device 300 illustrated in FIG. 4are described in Embodiment 1 and are thus omitted here.

FIG. 16 illustrates an example of cross-sections of part of a regionincluding the FPC 372, part of a region including the circuit 364, andpart of a region including the display portion 362 of the display device300 illustrated in FIG. 4.

In the display device 300 illustrated in FIG. 16, the width of theopening 451 is larger and the thickness of the insulating layer 220 issmaller than those in the display device 300 illustrated in FIG. 5. Thedisplay device 300 illustrated in FIG. 16 has a wider viewing angle thanthe display device 300 illustrated in FIG. 5; thus, a reduction incontrast and a change in chromaticity are less likely to occur even whenthe display device is seen from an oblique direction.

FIG. 17 is a cross-sectional view of the display device 300A. FIG. 18Ais a cross-sectional view of the display device 300B. FIG. 18B is across-sectional view of the display device 300C.

In the display device 300A illustrated in FIG. 17, the width of theopening 451 is larger and the thickness of the insulating layer 220 issmaller than those in the display device 300A illustrated in FIG. 6. Thesame applies to the comparison between the display device 300Billustrated in FIG. 18A and the display device 300B illustrated in FIG.7A and to the comparison between the display device 300C illustrated inFIG. 18B and the display device 300C illustrated in FIG. 7B.

Like in the display device illustrated in FIG. 16, each of the displaydevices illustrated in FIG. 17 and FIGS. 18A and 18B has a wide viewingangle; thus, a reduction in contrast and a change in chromaticity areless likely to occur even when the display device is seen from anoblique direction.

The display device of this embodiment can be fabricated by a methoddescribed as an example in Embodiment 1.

The display device of this embodiment includes two types of displayelements as described above; thus, switching between a plurality ofdisplay modes is possible. Accordingly, the display device can have highvisibility regardless of the ambient brightness, leading to highconvenience.

The display device of this embodiment has a wide viewing angle; thus,even when the display device is seen from an oblique direction, contrastis less likely to be reduced and chromaticity is less likely to change.Thus, information displayed on the display device can be recognized evenwhen the display device is seen from the direction greatly inclined withrespect to the display device.

This embodiment can be combined with any other embodiment asappropriate.

Embodiment 3

In this embodiment, the display device of one embodiment of the presentinvention will be described with reference to FIG. 19, FIGS. 20A to 20C,FIGS. 21A to 21C, and FIGS. 22A to 22C.

The display device of this embodiment includes a plurality of firstpixels including first display elements and a plurality of second pixelsincluding second display elements. The first pixels and the secondpixels are preferably arranged in matrices.

Each of the first pixels and the second pixels can include one or moresub-pixels. For example, each pixel can include one sub-pixel (e.g., awhite (W) sub-pixel), three sub-pixels (e.g., red (R), green (G), andblue (B) sub-pixels, or yellow (Y), cyan (C), and magenta (M)sub-pixels), or four sub-pixels (e.g., red (R), green (G), blue (B), andwhite (W) sub-pixels, or red (R), green (G), blue (B), and yellow (Y)sub-pixels).

The display device of this embodiment can display a full-color imageusing either the first pixels or the second pixels. Alternatively, thedisplay device of this embodiment can display a black-and-white image ora grayscale image using the first pixels and can display a full-colorimage using the second pixels. The first pixels that can be used fordisplaying a black-and-white image or a grayscale image is suitable fordisplaying information that need not be displayed in color such as textinformation.

FIG. 19 is a block diagram of the display device 10. The display device10 includes a display portion 14.

The display portion 14 includes a plurality of pixel units 30 arrangedin a matrix. The pixel units 30 each include a first pixel 31 p and asecond pixel 32 p.

FIG. 19 illustrates an example where the first pixel 31 p and the secondpixel 32 p each include display elements corresponding to three colorsof red (R), green (G), and blue (B).

The display elements included in the first pixel 31 p are each a displayelement that utilizes reflection of external light. The first pixel 31 pincludes a first display element 31R corresponding to red (R), a firstdisplay element 31G corresponding to green (G), and a first displayelement 31B corresponding to blue (B).

The display elements included in the second pixel 32 p are each alight-emitting element. The second pixel 32 p includes a second displayelement 32R corresponding to red (R), a second display element 32Gcorresponding to green (G), and a second display element 32Bcorresponding to blue (B).

FIGS. 20A to 20C are schematic views illustrating a structure example ofthe pixel unit 30.

The first pixel 31 p includes the first display element 31R, the firstdisplay element 31G, and the first display element 31B. The firstdisplay element 31R reflects external light and emits red light Rr tothe display surface side. Similarly, the first display element 31G andthe first display element 31B emit green light Gr and blue light Br,respectively, to the display surface side.

The second pixel 32 p includes the second display element 32R, thesecond display element 32G, and the second display element 32B. Thesecond display element 32R emits red light Rt to the display surfaceside. Similarly, the second display element 32G and the second displayelement 32B emit green light Gt and blue light Bt, respectively, to thedisplay surface side.

FIG. 20A corresponds to a display mode (third mode) in which both thefirst pixel 31 p and the second pixel 32 p are driven. The pixel unit 30can emit light 35 tr of a predetermined color to the display surfaceside using the reflected light (the light Rr, the light Gr, and thelight Br) and the transmitted light (the light Rt, the light Gt, and thelight Bt).

FIG. 20B corresponds to a display mode (first mode) using reflectedlight in which only the first pixel 31 p is driven. For example, whenthe intensity of external light is high enough, the pixel unit 30 canemit light 35 r to the display surface side using only the light fromthe first pixel 31 p (the light Rr, the light Gr, and the light Br),without driving the second pixel 32 p. Thus, driving with extremely lowpower consumption can be performed.

FIG. 20C corresponds to a display mode (second mode) using generatedlight (transmitted light) in which only the second pixel 32 p is driven.For example, when the intensity of external light is extremely low, thepixel unit 30 can emit light 35 t to the display surface side using onlythe light from the second pixel 32 p (the light Rt, the light Gt, andthe light Bt), without driving the first pixel 31 p. Thus, a vivid imagecan be displayed. Furthermore, by lowering the luminance in a darkenvironment, a user can be prevented from feeling glare and powerconsumption can be reduced.

There is no limitation on the color and number of display elementsincluded in the first pixel 31 p and the second pixel 32 p.

FIGS. 21A to 21C and FIGS. 22A to 22C each illustrate a structureexample of the pixel unit 30. Although FIGS. 21A to 21C and FIGS. 22A to22C are schematic views corresponding to the display mode (third mode)in which both the first pixel 31 p and the second pixel 32 p are driven,an image can be displayed in the mode (first mode or second mode) inwhich only the first pixel 31 p or the second pixel 32 p is driven, likethe above-described structure example.

The second pixel 32 p illustrated in FIGS. 21A and 21C and FIG. 22Bincludes a second display element 32W emitting white (W) light inaddition to the second display element 32R, the second display element32G, and the second display element 32B.

The second pixel 32 p illustrated in FIG. 21B and FIG. 22C includes asecond display element 32Y emitting yellow (Y) light in addition to thesecond display element 32R, the second display element 32G, and thesecond display element 32B.

Power consumption in the display mode using the second pixel 32 p(second mode and third mode) can be lower in the structures illustratedin FIGS. 21A to 21C and FIGS. 22B and 22C than in the structure notincluding the second display element 32W or the second display element32Y.

The first pixel 31 p illustrated in FIG. 21C includes a first displayelement 31W emitting white (W) light in addition to the first displayelement 31R, the first display element 31G, and the first displayelement 31B.

Power consumption in the display mode using the first pixel 31 p (firstmode and third mode) can be lower in the structure illustrated in FIG.21C than in the structure illustrated in FIG. 20A.

The first pixel 31 p illustrated in FIGS. 22A to 22C includes only thefirst display element 31W emitting white (W) light. In this structure, ablack-and-white image or a grayscale image can be displayed in thedisplay mode (first mode) using only the first pixel 31 p, and a colorimage can be displayed in the display mode (second mode and third mode)using the second pixel 32 p.

This structure can increase the aperture ratio of the first pixel 31 pand thus increase the reflectivity of the first pixel 31 p; accordingly,a brighter image can be displayed.

The first mode is suitable for displaying information that need not bedisplayed in color such as text information.

This embodiment can be combined with any other embodiment asappropriate.

Embodiment 4

In this embodiment, more specific structure examples of the displaydevice described in Embodiment 1 will be described with reference toFIGS. 23A, 23B1, 23B2, 23B3, and 23B4, FIG. 24, and FIGS. 25A and 25B.

FIG. 23A is a block diagram of a display device 400. The display device400 includes the display portion 362, a circuit GD, and a circuit SD.The display portion 362 includes a plurality of pixels 410 arranged in amatrix.

The display device 400 includes a plurality of wirings G1, a pluralityof wirings G2, a plurality of wirings ANO, a plurality of wirings CSCOM,a plurality of wirings S1, and a plurality of wirings S2. The pluralityof wirings G1, the plurality of wirings G2, the plurality of wiringsANO, and the plurality of wirings CSCOM are each electrically connectedto the circuit GD and the plurality of pixels 410 arranged in adirection indicated by an arrow R. The plurality of wirings S1 and theplurality of wirings S2 are each electrically connected to the circuitSD and the plurality of pixels 410 arranged in a direction indicated byan arrow C.

Although the structure including one circuit GD and one circuit SD isillustrated here for simplicity, the circuit GD and the circuit SD fordriving liquid crystal elements and the circuit GD and the circuit SDfor driving light-emitting elements may be provided separately.

The pixels 410 each include a reflective liquid crystal element and alight-emitting element.

FIGS. 23B1, 23B2, 23B3, and 23B4 illustrate structure examples of theelectrode 311 included in the pixel 410. The electrode 311 serves as areflective electrode of the liquid crystal element. The opening 451 isprovided in the electrode 311 in FIGS. 23B1 and 23B2.

In FIGS. 23B1 and 23B2, a light-emitting element 360 positioned in aregion overlapping with the electrode 311 is indicated by a broken line.The light-emitting element 360 overlaps with the opening 451 included inthe electrode 311. Thus, light from the light-emitting element 360 isemitted to the display surface side through the opening 451.

In FIG. 23B1, the pixels 410 which are adjacent in the directionindicated by the arrow R are pixels emitting light of different colors.As illustrated in FIG. 23B1, the openings 451 are preferably provided indifferent positions in the electrodes 311 so as not to be aligned in twoadjacent pixels provided in the direction indicated by the arrow R. Thisallows two light-emitting elements 360 to be apart from each other,thereby preventing light emitted from the light-emitting element 360from entering a coloring layer in the adjacent pixel 410 (such aphenomenon is referred to as crosstalk). Furthermore, since two adjacentlight-emitting elements 360 can be arranged apart from each other, ahigh-resolution display device is achieved even when EL layers of thelight-emitting elements 360 are separately formed with a shadow mask orthe like.

In FIG. 23B2, the pixels 410 which are adjacent in a direction indicatedby the arrow C are pixels emitting light of different colors. Also inFIG. 23B2, the openings 451 are preferably provided in differentpositions in the electrodes 311 so as not to be aligned in two adjacentpixels provided in the direction indicated by the arrow C.

The smaller the ratio of the total area of the opening 451 to the totalarea except for the opening is, the brighter an image displayed usingthe liquid crystal element can be. Furthermore, the larger the ratio ofthe total area of the opening 451 to the total area except for theopening is, the brighter an image displayed using the light-emittingelement 360 can be.

The opening 451 may have a polygonal shape, a quadrangular shape, anelliptical shape, a circular shape, a cross-like shape, a stripe shape,a slit-like shape, or a checkered pattern, for example. The opening 451may be provided close to the adjacent pixel. Preferably, the opening 451is provided close to another pixel emitting light of the same color, inwhich case crosstalk can be suppressed.

As illustrated in FIGS. 23B3 and 23B4, a light-emitting region of thelight-emitting element 360 may be positioned in a region where theelectrode 311 is not provided, in which case light emitted from thelight-emitting element 360 is emitted to the display surface side.

In FIG. 23B3, the light-emitting elements 360 are not aligned in twoadjacent pixels 410 provided in the direction indicated by the arrow R.In FIG. 23B4, the light-emitting elements 360 are aligned in twoadjacent pixels 410 provided in the direction indicated by the arrow R.

The structure illustrated in FIG. 23B3 can, as mentioned above, preventcrosstalk and increase the resolution because the light-emittingelements 360 included in two adjacent pixels 410 can be apart from eachother. The structure illustrated in FIG. 23B4 can prevent light emittedfrom the light-emitting element 360 from being blocked by the electrode311 because the electrode 311 is not positioned along a side of thelight-emitting element 360 which is parallel to the direction indicatedby the arrow C. Thus, high viewing angle characteristics can beachieved.

As the circuit GD, any of a variety of sequential circuits such as ashift register can be used. In the circuit GD, a transistor, acapacitor, and the like can be used. A transistor included in thecircuit GD can be formed in the same steps as the transistors includedin the pixels 410.

The circuit SD is electrically connected to the wirings S1. For example,an integrated circuit can be used as the circuit SD. Specifically, anintegrated circuit formed on a silicon substrate can be used as thecircuit SD.

For example, a chip on glass (COG) method, a COF method, or the like canbe used to mount the circuit SD on a pad electrically connected to thepixels 410. Specifically, an anisotropic conductive film can be used tomount an integrated circuit on the pad.

FIG. 24 is an example of a circuit diagram of the pixels 410. FIG. 24illustrates two adjacent pixels 410.

The pixels 410 each include a switch SW1, a capacitor C1, a liquidcrystal element 340, a switch SW2, a transistor M, a capacitor C2, thelight-emitting element 360, and the like. The pixel 410 is electricallyconnected to the wiring G1, the wiring G2, the wiring ANO, the wiringCSCOM, the wiring S1, and the wiring S2. FIG. 24 illustrates a wiringVCOM1 electrically connected to the liquid crystal element 340 and awiring VCOM2 electrically connected to the light-emitting element 360.

FIG. 24 illustrates an example in which a transistor is used as each ofthe switches SW1 and SW2.

A gate of the switch SW1 is connected to the wiring G1. One of a sourceand a drain of the switch SW1 is connected to the wiring S1, and theother is connected to one electrode of the capacitor C1 and oneelectrode of the liquid crystal element 340. The other electrode of thecapacitor C1 is connected to the wiring CSCOM. The other electrode ofthe liquid crystal element 340 is connected to the wiring VCOM1.

A gate of the switch SW2 is connected to the wiring G2. One of a sourceand a drain of the switch SW2 is connected to the wiring S2, and theother is connected to one electrode of the capacitor C2 and gates of thetransistor M. The other electrode of the capacitor C2 is connected toone of a source and a drain of the transistor M and the wiring ANO. Theother of the source and the drain of the transistor M is connected toone electrode of the light-emitting element 360. Furthermore, the otherelectrode of the light-emitting element 360 is connected to the wiringVCOM2.

FIG. 24 illustrates an example where the transistor M includes two gatesbetween which a semiconductor is provided and which are connected toeach other. This structure can increase the amount of current flowingthrough the transistor M.

The wiring G1 can be supplied with a signal for changing the on/offstate of the switch SW1. A predetermined potential can be supplied tothe wiring VCOM1. The wiring S1 can be supplied with a signal forchanging the orientation of liquid crystals of the liquid crystalelement 340. A predetermined potential can be supplied to the wiringCSCOM.

The wiring G2 can be supplied with a signal for changing the on/offstate of the switch SW2. The wiring VCOM2 and the wiring ANO can besupplied with potentials having a difference large enough to make thelight-emitting element 360 emit light. The wiring S2 can be suppliedwith a signal for changing the conduction state of the transistor M.

In the pixel 410 of FIG. 24, for example, an image can be displayed inthe reflective mode by driving the pixel with the signals supplied tothe wiring G1 and the wiring S1 and utilizing the optical modulation ofthe liquid crystal element 340. In the case where an image is displayedin the transmissive mode, the pixel is driven with the signals suppliedto the wiring G2 and the wiring S2 and the light-emitting element 360emits light. In the case where both modes are performed at the sametime, the pixel can be driven with the signals supplied to the wiringG1, the wiring G2, the wiring S1, and the wiring S2.

Although FIG. 24 illustrates an example in which one liquid crystalelement 340 and one light-emitting element 360 are provided in one pixel410, one embodiment of the present invention is not limited thereto.FIG. 25A illustrates an example in which one liquid crystal element 340and four light-emitting elements 360 (light-emitting elements 360 r, 360g, 360 b, and 360 w) are provided in one pixel 410. The pixel 410illustrated in FIG. 25A differs from that in FIG. 24 in being capable ofdisplaying a full-color image with the use of the light-emittingelements by one pixel.

In FIG. 25A, in addition to the wirings in FIG. 24, a wiring G3 and awiring S3 are connected to the pixel 410.

In the example in FIG. 25A, light-emitting elements emitting red light(R), green light (G), blue light (B), and white light (W) can be used asthe four light-emitting elements 360, for example. Furthermore, as theliquid crystal element 340, a reflective liquid crystal element emittingwhite light can be used. Thus, in the case of displaying an image in thereflective mode, a white image can be displayed with high reflectivity.In the case of displaying an image in the transmissive mode, an imagecan be displayed with a higher color rendering property at low powerconsumption.

FIG. 25B illustrates a structure example of the pixel 410 correspondingto FIG. 25A. The pixel 410 includes the light-emitting element 360 woverlapping with the opening included in the electrode 311 and thelight-emitting element 360 r, the light-emitting element 360 g, and thelight-emitting element 360 b which are arranged in the periphery of theelectrode 311. It is preferable that the light-emitting elements 360 r,360 g, and 360 b have almost the same light-emitting area.

This embodiment can be combined with any other embodiment asappropriate.

Embodiment 5

In this embodiment, described below is the composition of acloud-aligned composite oxide semiconductor (CAC-OS) applicable to atransistor disclosed in one embodiment of the present invention.

The CAC-OS refers to, for example, a composition of a material in whichelements included in an oxide semiconductor are unevenly distributed.The material including unevenly distributed elements has a size ofgreater than or equal to 0.5 nm and less than or equal to 10 nm,preferably greater than or equal to 1 nm and less than or equal to 2 nm,or a similar size. Note that in the following description of an oxidesemiconductor, a state in which one or more metal elements are unevenlydistributed and regions including the metal element(s) are mixed isreferred to as a mosaic pattern or a patch-like pattern. The region hasa size of greater than or equal to 0.5 nm and less than or equal to 10nm, preferably greater than or equal to 1 nm and less than or equal to 2nm, or a similar size.

Note that an oxide semiconductor preferably contains at least indium. Inparticular, indium and zinc are preferably contained. In addition, oneor more of, aluminum, gallium, yttrium, copper, vanadium, beryllium,boron, silicon, titanium, iron, nickel, germanium, zirconium,molybdenum, lanthanum, cerium, neodymium, hafnium, tantalum, tungsten,magnesium, and the like may be contained.

For example, of the CAC-OS, an In—Ga—Zn oxide with the CAC composition(such an In—Ga—Zn oxide may be particularly referred to as CAC-IGZO) hasa composition in which indium oxide (InO_(X1), where X1 is a real numbergreater than 0) or indium zinc oxide (In_(X2)Zn_(Y2)O_(Z2), where X2,Y2, and Z2 are real numbers greater than 0) forming a mosaic pattern isevenly distributed in the film (this composition is also referred to asa cloud-like composition). The mosaic pattern is formed by separatingthe materials into InO_(X1) or In_(X2)Zn_(Y2)O_(Z2) and gallium oxide(GaO_(X3), where X3 is a real number greater than 0) or gallium zincoxide (Ga_(X4)Zn_(Y4)O_(Z4), where X4, Y4, and Z4 are real numbersgreater than 0), for example.

That is, the CAC-OS is a composite oxide semiconductor with acomposition in which a region including GaO_(X3) as a main component anda region including In_(X2)Zn_(Y2)O_(Z2) or InO_(X1) as a main componentare mixed. Note that in this specification, for example, when the atomicratio of In to an element M in a first region is greater than the atomicratio of In to an element M in a second region, the first region isdescribed as having higher In concentration than the second region.

Note that a compound including In, Ga, Zn, and O is also known as IGZO.Typical examples of IGZO include a crystalline compound represented byInGaO₃(ZnO)_(m1) (ml is a natural number) and a crystalline compoundrepresented by In_((1+x0))Ga_((1−x0))O₃(ZnO)_(m0) (−≦x0≦1; m0 is a givennumber).

The above crystalline compounds have a single crystal structure, apolycrystalline structure, or a CAAC structure. Note that the CAACstructure is a crystal structure in which a plurality of IGZOnanocrystals have c-axis alignment and are connected in the a-b planedirection without alignment.

The CAC-OS relates to the material composition of an oxidesemiconductor. In a material composition of a CAC-OS including In, Ga,Zn, and O, nanoparticle regions including Ga as a main component areobserved in part of the CAC-OS and nanoparticle regions including In asa main component are observed in part thereof. These nanoparticleregions are randomly dispersed to form a mosaic pattern. Therefore, thecrystal structure is a secondary element for the CAC-OS.

Note that in the CAC-OS, a stacked-layer structure of two or more filmswith different atomic ratios is not included. For example, a two-layerstructure of a film including In as a main component and a filmincluding Ga as a main component is not included.

A boundary between the region including GaO_(X3) as a main component andthe region including In_(X2)Zn_(Y2)O_(Z2) or InO_(X1) as a maincomponent is not clearly observed in some cases.

In the case where one or more of aluminum, yttrium, copper, vanadium,beryllium, boron, silicon, titanium, iron, nickel, germanium, zirconium,molybdenum, lanthanum, cerium, neodymium, hafnium, tantalum, tungsten,magnesium, and the like are contained instead of gallium in a CAC-OS,nanoparticle regions including the selected element(s) as a maincomponent(s) are observed in part of the CAC-OS and nanoparticle regionsincluding In as a main component are observed in part of the CAC-OS, andthese nanoparticle regions are randomly dispersed to form a mosaicpattern in the CAC-OS.

The CAC-OS can be formed by a sputtering method under a condition wherea substrate is not heated intentionally. In the case where the CAC-OS isformed by a sputtering method, one or more of an inert gas (typically,argon), an oxygen gas, and a nitrogen gas can be used as a depositiongas. Furthermore, the flow rate of the oxygen gas to the total flow rateof the deposition gas in deposition is preferably as low as possible,for example, the flow rate of the oxygen gas is higher than equal to 0%and lower than 30%, preferably higher than equal to 0% and lower than orequal to 10%.

The CAC-OS is characterized in that a clear peak is not observed whenmeasurement is conducted using a θ/2θ scan by an out-of-plane methodwith an X-ray diffraction (XRD). That is, it is found by the XRD thatthere are no alignment in the a-b plane direction and no alignment inthe c-axis direction in the measured areas.

In the CAC-OS, an electron diffraction pattern that is obtained byirradiation with an electron beam with a probe diameter of 1 nm (alsoreferred to as nanobeam electron beam) has regions with high luminancein a ring pattern and a plurality of bright spots appear in thering-like pattern. Thus, it is found from the electron diffractionpattern that the crystal structure of the CAC-OS includes ananocrystalline (nc) structure that does not show alignment in the planedirection and the cross-sectional direction.

For example, energy dispersive X-ray spectroscopy (EDX) is used toobtain EDX mapping, and according to the EDX mapping, the CAC-OS of theIn—Ga—Zn oxide has a composition in which the regions including GaO_(X3)as a main component and the regions including In_(X2)Zn_(Y2)O_(Z2) orInO_(X1) as a main component are unevenly distributed and mixed.

The CAC-OS has a structure different from that of an IGZO compound inwhich metal elements are evenly distributed, and has characteristicsdifferent from those of the IGZO compound. That is, in the CAC-OS,regions including GaO_(X3) or the like as a main component and regionsincluding In_(X2)Zn_(Y2)O_(Z2) or InO_(X1) as a main component areseparated to form a mosaic pattern.

The conductivity of a region including In_(X2)Zn_(Y2)O_(Z2) or InO_(X1)as a main component is higher than that of a region including GaO_(X3)or the like as a main component. In other words, when carriers flowthrough regions including In_(X2)Zn_(Y2)O_(Z2) or InO_(n) as a maincomponent, the conductivity of an oxide semiconductor is generated.Accordingly, when regions including In_(X2)Zn_(Y2)O_(Z2) or InO_(X1) asa main component are distributed in an oxide semiconductor like a cloud,high field-effect mobility (μ) can be achieved.

In contrast, the insulating property of a region including GaO_(X3) orthe like as a main component is higher than that of a region includingIn_(X2)Zn_(Y2)O_(Z2) or InO_(X1) as a main component. In other words,when regions including GaO_(X3) or the like as a main component aredistributed in an oxide semiconductor, leakage current can be suppressedand favorable switching operation can be achieved.

Accordingly, when a CAC-OS is used in a semiconductor element, theinsulating property derived from GaO_(X3) or the like and theconductivity derived from In_(X2)Zn_(Y2)O_(Z2) or InO_(X1) complementeach other, whereby high on-state current (I_(on)) and high field-effectmobility (μ) can be achieved.

A semiconductor element including a CAC-OS has high reliability. Thus,the CAC-OS is suitably used in a variety of semiconductor devicestypified by a display.

This embodiment can be combined with any other embodiment asappropriate.

Embodiment 6

In this embodiment, a display module and electronic devices ofembodiments of the present invention are described.

In a display module 8000 in FIG. 26, a touch panel 8004 connected to anFPC 8003, a display panel 8006 connected to an FPC 8005, a frame 8009, aprinted circuit board 8010, and a battery 8011 are provided between anupper cover 8001 and a lower cover 8002.

The display device of one embodiment of the present invention can beused for, for example, the display panel 8006. In that case, a displaymodule with high visibility regardless of the ambient brightness, adisplay module with low power consumption, or a display module with awide viewing angle can be fabricated.

The shape and size of the upper cover 8001 and the lower cover 8002 canbe changed as appropriate in accordance with the sizes of the touchpanel 8004 and the display panel 8006.

The touch panel 8004 can be a resistive touch panel or a capacitivetouch panel and can be formed to overlap with the display panel 8006.Instead of providing the touch panel 8004, the display panel 8006 canhave a touch panel function.

The frame 8009 protects the display panel 8006 and functions as anelectromagnetic shield for blocking electromagnetic waves generated bythe operation of the printed circuit board 8010. The frame 8009 can alsofunction as a radiator plate.

The printed circuit board 8010 includes a power supply circuit and asignal processing circuit for outputting a video signal and a clocksignal. As a power source for supplying power to the power supplycircuit, an external commercial power source or the battery 8011provided separately may be used. The battery 8011 can be omitted in thecase of using a commercial power source.

The display module 8000 may be additionally provided with a member suchas a polarizing plate, a retardation plate, or a prism sheet.

The display device of one embodiment of the present invention canachieve high visibility regardless of the intensity of external light.Thus, the display device of one embodiment of the present invention canbe suitably used for a portable electronic device, a wearable electronicdevice (wearable device), an e-book reader, or the like.

The display device of one embodiment of the present invention has a wideviewing angle. Thus, the display device can be suitably used for largedisplay portions of television devices, monitors of computers and thelike, digital signage, and PIDs, for example.

A portable information terminal 800 illustrated in FIGS. 27A and 27Bincludes a housing 801, a housing 802, a display portion 803, a displayportion 804, a hinge portion 805, and the like.

The housing 801 and the housing 802 are joined together with the hingeportion 805. The portable information terminal 800 can be opened asillustrated in FIG. 27B from a closed state (FIG. 27A).

The display device of one embodiment of the present invention can beused for at least one of the display portion 803 and the display portion804. In that case, a portable information terminal with high visibilityregardless of the ambient brightness, a portable information terminalwith low power consumption, or a portable information terminal with awide viewing angle can be fabricated. When a plurality of viewers lookat the display portion of the portable information terminal from variousangles at the same time, information displayed on the display portioncan be recognized by the viewers.

The display portion 803 and the display portion 804 can each display atleast one of a text, a still image, a moving image, and the like. When atext is displayed on the display portion, the portable informationterminal 800 can be used as an e-book reader.

Since the portable information terminal 800 is foldable, the portableinformation terminal 800 has high portability and excellent versatility.

A power button, an operation button, an external connection port, aspeaker, a microphone, or the like may be provided for the housing 801and the housing 802.

A portable information terminal 810 illustrated in FIG. 27C includes ahousing 811, a display portion 812, an operation button 813, an externalconnection port 814, a speaker 815, a microphone 816, a camera 817, andthe like.

The display device of one embodiment of the present invention can beused for the display portion 812. In that case, a portable informationterminal with high visibility regardless of the ambient brightness, aportable information terminal with low power consumption, or a portableinformation terminal with a wide viewing angle can be fabricated. When aplurality of viewers look at the display portion of the portableinformation terminal from various angles at the same time, informationdisplayed on the display portion can be recognized by the viewers.

The portable information terminal 810 includes a touch sensor in thedisplay portion 812. Operations such as making a call and inputting acharacter can be performed by touch on the display portion 812 with afinger, a stylus, or the like.

With the operation button 813, the power can be turned on or off Inaddition, types of images displayed on the display portion 812 can beswitched; for example, switching an image from a mail creation screen toa main menu screen is performed with the operation button 813.

When a detection device such as a gyroscope sensor or an accelerationsensor is provided inside the portable information terminal 810, thedirection of display on the screen of the display portion 812 can beautomatically changed by determining the orientation of the portableinformation terminal 810 (whether the portable information terminal 810is placed horizontally or vertically). Furthermore, the direction ofdisplay on the screen can be changed by touch on the display portion812, operation with the operation button 813, sound input using themicrophone 816, or the like.

The portable information terminal 810 functions as, for example, one ormore of a telephone set, a notebook, and an information browsing system.Specifically, the portable information terminal 810 can be used as asmartphone. The portable information terminal 810 is capable ofexecuting a variety of applications such as mobile phone calls,e-mailing, viewing and editing texts, music reproduction, reproducing amoving image, Internet communication, and computer games, for example.

A camera 820 illustrated in FIG. 27D includes a housing 821, a displayportion 822, operation buttons 823, a shutter button 824, and the like.Furthermore, an attachable lens 826 is attached to the camera 820.

The display device of one embodiment of the present invention can beused for the display portion 822. The use of the display portion withhigh visibility regardless of the ambient brightness can increase theconvenience of the camera. Furthermore, a camera with low powerconsumption or a camera with a wide viewing angle can be fabricated.When a plurality of viewers look at the display portion of the camerafrom various angles at the same time, information displayed on thedisplay portion can be recognized by the viewers.

Although the lens 826 of the camera 820 here is detachable from thehousing 821 for replacement, the lens 826 may be incorporated into thehousing 821.

A still image or a moving image can be taken with the camera 820 at thepress of the shutter button 824. In addition, images can also be takenby the touch of the display portion 822 which serves as a touch panel.

Note that a stroboscope, a viewfinder, or the like can be additionallyattached to the camera 820. Alternatively, these may be incorporatedinto the housing 821.

FIGS. 28A to 28E illustrate electronic devices. These electronic deviceseach include a housing 9000, a display portion 9001, a speaker 9003, anoperation key 9005 (including a power switch or an operation switch), aconnection terminal 9006, a sensor 9007 (a sensor having a function ofmeasuring force, displacement, position, speed, acceleration, angularvelocity, rotational frequency, distance, light, liquid, magnetism,temperature, chemical substance, sound, time, hardness, electric field,current, voltage, power, radiation, flow rate, humidity, gradient,oscillation, odor, or infrared rays), a microphone 9008, and the like.

The display device of one embodiment of the present invention can besuitably used for the display portion 9001. Thus, an electronic deviceincluding a display portion with high visibility regardless of thesurrounding brightness can be manufactured. Furthermore, an electronicdevice with low power consumption or an electronic device with a wideviewing angle can be fabricated.

The electronic devices illustrated in FIGS. 28A to 28E can have avariety of functions, for example, a function of displaying a variety ofinformation (a still image, a moving image, a text image, and the like)on the display portion, a touch panel function, a function of displayinga calendar, the date, the time, and the like, a function of controllingprocessing with a variety of software (programs), a wirelesscommunication function, a function of being connected to a variety ofcomputer networks with a wireless communication function, a function oftransmitting and receiving a variety of data with a wirelesscommunication function, a function of reading a program or data storedin a storage medium and displaying the program or data on the displayportion, and the like. Note that the functions of the electronic devicesillustrated in FIGS. 28A to 28E are not limited to the above, and theelectronic devices may have other functions.

FIG. 28A is a perspective view of a watch-type portable informationterminal 9200. FIG. 28B is a perspective view of a watch-type portableinformation terminal 9201.

The portable information terminal 9200 illustrated in FIG. 28A iscapable of executing a variety of applications such as mobile phonecalls, e-mailing, viewing and editing texts, music reproduction,Internet communication, and computer games. The display surface of thedisplay portion 9001 is bent, and an image can be displayed on the bentdisplay surface. The portable information terminal 9200 can employ nearfield communication conformable to a communication standard. In thatcase, for example, mutual communication between the portable informationterminal 9200 and a headset capable of wireless communication can beperformed, and thus hands-free calling is possible. The portableinformation terminal 9200 includes the connection terminal 9006, anddata can be directly transmitted to and received from anotherinformation terminal via a connector. Power charging through theconnection terminal 9006 is also possible. Note that the chargingoperation may be performed by wireless power feeding without using theconnection terminal 9006.

Unlike in the portable information terminal illustrated in FIG. 28A, thedisplay surface of the display portion 9001 is not curved in theportable information terminal 9201 illustrated in FIG. 28B. Furthermore,the external state of the display portion of the portable informationterminal 9201 is a non-rectangular shape (a circular shape in FIG. 28B).

FIGS. 28C to 28E are perspective views of a foldable portableinformation terminal 9202. FIG. 28C is a perspective view illustratingthe portable information terminal 9202 that is opened. FIG. 28D is aperspective view illustrating the portable information terminal 9202that is being opened or being folded. FIG. 28E is a perspective viewillustrating the portable information terminal 9202 that is folded.

The folded portable information terminal 9202 is highly portable, andthe opened portable information terminal 9202 is highly browsable due toa seamless large display region. The display portion 9001 of theportable information terminal 9202 is supported by three housings 9000joined together by hinges 9055. By folding the portable informationterminal 9202 at a connection portion between two housings 9000 with thehinges 9055, the portable information terminal 9202 can be reversiblychanged in shape from opened to folded. For example, the portableinformation terminal 9202 can be bent with a radius of curvature ofgreater than or equal to 1 mm and less than or equal to 150 mm.

This embodiment can be combined with any other embodiment asappropriate.

This application is based on Japanese Patent Application serial No.2016-130007 filed with Japan Patent Office on Jun. 30, 2016 and JapanesePatent Application serial No. 2016-136220 filed with Japan Patent Officeon Jul. 8, 2016, the entire contents of which are hereby incorporated byreference.

What is claimed is:
 1. A display device comprising: a first displayelement; a second display element; and an insulating layer, wherein thefirst display element includes a first pixel electrode configured toreflect visible light, wherein the second display element is configuredto emit visible light, wherein the second display element includes asecond pixel electrode and a common electrode, wherein the first pixelelectrode is positioned on an opposite side of the insulating layer fromthe second pixel electrode, wherein the common electrode is positionedon an opposite side of the second pixel electrode from the insulatinglayer, wherein a shortest distance X between a first plane and a secondplane is longer than or equal to 500 nm and shorter than or equal to 200μm, wherein the first plane includes a plane of the first pixelelectrode on the insulating layer side in a display region of the firstdisplay element, and wherein the second plane includes a plane of thecommon electrode on the insulating layer side in a display region of thesecond display element.
 2. The display device according to claim 1,further comprising: a first transistor; and a second transistor, whereinthe first transistor is configured to control driving of the firstdisplay element, wherein the second transistor is configured to controldriving of the second display element, and wherein the insulating layerhas a portion serving as a gate insulating layer of the first transistorand a portion serving as a gate insulating layer of the secondtransistor.
 3. The display device according to claim 1, wherein theshortest distance X is longer than or equal to 1 μm and shorter than orequal to 20 μm.
 4. The display device according to claim 1, wherein thefirst pixel electrode includes an opening, wherein the second displayelement includes a region overlapping with the opening, and wherein thesecond display element is configured to emit visible light to theopening.
 5. The display device according to claim 1, wherein the displaydevice is configured to display an image using one or both of lightreflected by the first display element and light emitted from the seconddisplay element.
 6. The display device according to claim 1, wherein thefirst display element is a reflective liquid crystal element.
 7. Thedisplay device according to claim 1, wherein the second display elementis an electroluminescent element.
 8. A display module comprising acircuit board and the display device according to claim
 1. 9. Anelectronic device comprising at least one of an antenna, a battery, ahousing, a camera, a speaker, a microphone and an operation button, andthe display module according to claim
 8. 10. A display devicecomprising: a first display element; a second display element; a firstinsulating layer; a second insulating layer; a first transistor; and asecond transistor, wherein the first transistor is configured to controldriving of the first display element, wherein the second transistor isconfigured to control driving of the second display element, wherein thefirst display element includes a first pixel electrode configured toreflect visible light, wherein the second display element is configuredto emit visible light, wherein the second display element includes asecond pixel electrode and a common electrode, wherein the firsttransistor and the second transistor are positioned between the firstinsulating layer and the second insulating layer, wherein the firsttransistor is electrically connected to the first pixel electrodethrough an opening in the first insulating layer, wherein the secondtransistor is electrically connected to the second pixel electrodethrough an opening in the second insulating layer, wherein the commonelectrode is positioned on an opposite side of the second pixelelectrode from the second insulating layer, wherein a shortest distanceX between a first plane and a second plane is longer than or equal to500 nm and shorter than or equal to 200 μm, wherein the first planeincludes a plane of the first pixel electrode on the first transistorside in a display region of the first display element, and wherein thesecond plane includes a plane of the common electrode on the secondtransistor side in a display region of the second display element. 11.The display device according to claim 10, wherein one or both of thefirst transistor and the second transistor include an oxidesemiconductor in a channel formation region.
 12. The display deviceaccording to claim 10, further comprising an optical member, wherein ashortest distance between the optical member and the first transistor islonger than a shortest distance between the optical member and the firstdisplay element, and wherein a shortest distance between the opticalmember and the second display element is longer than the shortestdistance between the optical member and the first transistor.
 13. Thedisplay device according to claim 12, wherein the optical memberincludes at least one of a polarizing plate, a light diffusion layer,and an anti-reflective layer.
 14. The display device according to claim10, wherein the shortest distance X is longer than or equal to 1 μm andshorter than or equal to 20 μm.
 15. The display device according toclaim 10, wherein the first pixel electrode includes an opening, whereinthe second display element includes a region overlapping with theopening, and wherein the second display element is configured to emitvisible light to the opening.
 16. The display device according to claim10, wherein the display device is configured to display an image usingone or both of light reflected by the first display element and lightemitted from the second display element.
 17. The display deviceaccording to claim 10, wherein the first display element is a reflectiveliquid crystal element.
 18. The display device according to claim 10,wherein the second display element is an electroluminescent element. 19.A display module comprising a circuit board and the display deviceaccording to claim
 10. 20. An electronic device comprising at least oneof an antenna, a battery, a housing, a camera, a speaker, a microphoneand an operation button, and the display module according to claim 19.21. A method for manufacturing a display device comprising a firstdisplay element, a second display element, and an insulating layer,comprising the steps of: forming a first common electrode over a firstsubstrate; forming a first pixel electrode over a formation substrate;forming the insulating layer over the first pixel electrode; forming thesecond display element; bonding the formation substrate and a secondsubstrate to each other with an adhesive; separating the formationsubstrate and the first pixel electrode from each other; and bonding thefirst substrate and the second substrate to each other with an adhesivewith a liquid crystal layer positioned between the first commonelectrode and the exposed first pixel electrode to form the firstdisplay element, wherein the first display element includes the firstpixel electrode configured to reflect visible light, the liquid crystallayer, and the first common electrode configured to transmit visiblelight, wherein the second display element includes a second pixelelectrode configured to transmit visible light, a light-emitting layer,and a second common electrode configured to reflect visible light,wherein the second display element is formed by forming the second pixelelectrode, the light-emitting layer, and the second common electrode inthis order over the insulating layer, wherein a shortest distance Xbetween a first plane and a second plane is longer than or equal to 500nm and shorter than or equal to 200 μm, and wherein the first planeincludes a plane of the first pixel electrode on the insulating layerside in a display region of the first display element, and the secondplane includes a plane of the second common electrode on the insulatinglayer side in a display region of the second display element.
 22. Themethod for manufacturing a display device according to claim 21, furthercomprising the steps of: providing an opening in the first pixelelectrode after the first pixel electrode is formed; and forming thesecond display element in a region overlapping with the opening.
 23. Themanufacturing method of a display device, according to claim 21, whereinthe adhesive used to bond the first substrate and the second substrateincludes a conductive particle, wherein first pixel electrode and aconductive layer are formed by processing one conductive film in thestep of forming the first pixel electrode, and wherein the first commonelectrode and the conductive layer are electrically connected to eachother by the conductive particle in the step of bonding the firstsubstrate and the second substrate to each other.
 24. A display devicecomprising: a first display element; a second display element; and aninsulating layer, wherein the first display element is configured toreflect visible light, wherein the second display element is configuredto emit visible light, wherein the first display element is positionedon an opposite side of the insulating layer from the second displayelement, wherein a viewer can see 10% or more of an area of a displayregion of the second display element when the viewer sees the displaydevice from a direction inclined by 85° from a direction perpendicularto a display surface of the display device, and wherein the viewer cansee 100% of an area of the display region of the second display elementwhen the viewer sees the display device from a direction inclined by 30°from the direction perpendicular to the display surface of the displaydevice.
 25. The display device according to claim 24, wherein the firstdisplay element includes a first pixel electrode configured to reflectvisible light, wherein the second display element includes a secondpixel electrode and a common electrode, wherein the first pixelelectrode is positioned on an opposite side of the insulating layer fromthe second pixel electrode, and wherein the common electrode ispositioned on an opposite side of the second pixel electrode from theinsulating layer.
 26. The display device according to claim 25, whereinthe first pixel electrode includes an opening, wherein the seconddisplay element includes a region overlapping with the opening, andwherein the second display element is configured to emit visible lightto the opening.
 27. The display device according to claim 26, wherein afirst plane includes a plane of the first pixel electrode on an oppositeside of the insulating layer in a display region of the first displayelement, wherein a second plane includes a plane of the common electrodeon the insulating layer side in a display region of the second displayelement, and wherein Formula (1), Formula (2), Formula (3), and Formula(4) are satisfied: $\begin{matrix}{{D\; \tan \; \theta_{1}} \leq {{\frac{9}{10}L} + A}} & (1) \\{\frac{\sin \; \theta_{1}}{\sin \; 85{^\circ}} = \frac{1}{N}} & (2) \\{{D\; \tan \; \theta_{2}} \leq A} & (3) \\{\frac{\sin \; \theta_{2}}{\sin \; 30{^\circ}} = \frac{1}{N}} & (4)\end{matrix}$ wherein A represents a length between an end portion ofthe first pixel electrode and a foot of a perpendicular drawn from anend portion of the display region of the second display element to thefirst plane; A is greater than or equal to 0; D represents a shortestdistance between the first plane and the second plane; L represents awidth of the second pixel electrode; N represents a refractive indexbetween the first plane and the second plane in the region overlappingwith the opening; N is greater than or equal to 1; and each of θ₁ and θ₂represents an angle formed by a perpendicular from the second plane tothe first plane and incident light from the second display element tothe first plane.
 28. The display device according to claim 27, wherein astacked-layer structure of a layers is between the first plane and thesecond plane and in the region overlapping with the opening, and whereinN satisfies Formula (5): $\begin{matrix}{N = \frac{\sum\limits_{x = 1}^{a}\; {N_{x}D_{x}}}{D}} & (5)\end{matrix}$ wherein a is an integer greater than or equal to 2; x isan integer greater than or equal to 1 and less than or equal to a; D_(x)represents a thickness of an x-th layer in the stacked-layer structure;N_(x) represents a refractive index of the x-th layer in thestacked-layer structure; and N_(x) is greater than or equal to
 1. 29.The display device according to claim 26, wherein a first plane includesa plane of the first pixel electrode on an opposite side of theinsulating layer in a display region of the first display element,wherein a second plane includes a plane of the common electrode on theinsulating layer side in a display region of the second display element,wherein a stacked-layer structure of a layers is between the first planeand the second plane and in the region overlapping with the opening, andwherein Formula (6), Formula (7), Formula (8), and Formula (9) aresatisfied: $\begin{matrix}{{\sum\limits_{x = 1}^{a}\; {D_{x}\; \tan \; \theta_{x}}} \leq {{\frac{9}{10}L} + A}} & (6) \\{\frac{\sin \; \theta_{x}}{\sin \; 85{^\circ}} = \frac{1}{N_{x}}} & (7) \\{{\sum\limits_{y = 1}^{a}\; {D_{y}\; \tan \; \theta_{y}}} \leq A} & (8) \\{\frac{\sin \; \theta_{y}}{\sin \; 30{^\circ}} = \frac{1}{N_{y}}} & (9)\end{matrix}$ wherein a is an integer greater than or equal to 2; eachof x and y is an integer greater than or equal to 1 and less than orequal to a; A represents a length between an end portion of the firstpixel electrode and a foot of a perpendicular drawn from an end portionof the display region of the second display element to the first plane;A is greater than or equal to 0; D_(x) represents a thickness of an x-thlayer in the stacked-layer structure; D_(y) represents a thickness of ay-th layer in the stacked-layer structure; L represents a width of thesecond pixel electrode; N_(x) represents a refractive index of the x-thlayer in the stacked-layer structure; N_(y) represents a refractiveindex of the y-th layer in the stacked-layer structure; each of N_(x)and N_(y) is greater than or equal to 1; θ_(x) represents an angleformed by a perpendicular from the second plane to the first plane andrefracted light of light emitted from the second display element thatenters the x-th layer from an (x−1)-th layer; θ_(y) represents an angleformed by the perpendicular from the second plane to the first plane andrefracted light of light emitted from the second display element thatenters the y-th layer from a (y−1)-th layer.
 30. The display deviceaccording to claim 24, further comprising: a first transistor; and asecond transistor, wherein the first transistor is configured to controldriving of the first display element, wherein the second transistor isconfigured to control driving of the second display element, and whereinthe insulating layer has a portion serving as a gate insulating layer ofthe first transistor and a portion serving as a gate insulating layer ofthe second transistor.
 31. The display device according to claim 30,wherein one or both of the first transistor and the second transistorinclude an oxide semiconductor in a channel formation region.
 32. Thedisplay device according to claim 30, further comprising an opticalmember, wherein a shortest distance between the optical member and thefirst transistor is longer than a shortest distance between the opticalmember and the first display element, and wherein a shortest distancebetween the optical member and the second display element is longer thanthe shortest distance between the optical member and the firsttransistor.
 33. The display device according to claim 32, wherein theoptical member includes at least one of a polarizing plate, a lightdiffusion layer, and an anti-reflective layer.